QUESTIONS AND ANSWERS

The following are some questions that you, as an Allegiance shareholder or a Post Oak shareholder, may have about the merger, the Allegiance special meeting and the Post Oak special meeting, as applicable, and brief answers to those questions. Allegiance and Post Oak urge you to read carefully the remainder of this joint proxy statement/prospectus because the information in this section does not provide all of the information that might be important to you with respect to the merger, the Allegiance special meeting and the Post Oak special meeting or the proposals presented at those meetings, as applicable. Additional important information is also contained in the annexes to this joint proxy statement/prospectus. For details about where you can find additional important information, please see the section of this joint proxy statement/prospectus entitled “Where You Can Find More Information” beginning on page 152.

Unless the context otherwise requires, references in this joint proxy statement/prospectus to “Allegiance” refer to Allegiance Bancshares, Inc., a Texas corporation, and its affiliates, including Allegiance Bank, a Texas state bank and a wholly-owned subsidiary of Allegiance (which we refer to as “Allegiance Bank”). Additionally, unless the context otherwise requires, references in this joint proxy statement/prospectus to “Post Oak” refer to Post Oak Bancshares, Inc., a Texas corporation, and its affiliates, including Post Oak Bank, N.A., a national banking association and a wholly-owned subsidiary of Post Oak (which we refer to as “Post Oak Bank”).

A copy of the merger agreement is included in this joint proxy statement/prospectus as Annex A.

The merger cannot be completed unless, among other things:

Allegiance has called a special meeting of its shareholders to consider and vote on the Allegiance Merger Proposal, the Allegiance Stock Issuance Proposal, the Allegiance Charter Amendment Proposal and other matters described herein. This document serves as the proxy statement for the Allegiance special meeting and describes the proposals to be presented at the Allegiance special meeting. This document also constitutes a notice of special meeting with respect to the Allegiance special meeting.

Post Oak has called a special meeting of its shareholders to consider the Post Oak Merger Proposal. This document serves as the proxy statement for the Post Oak special meeting and describes the proposals to be presented at the Post Oak special meeting. It also constitutes a notice of special meeting with respect to the Post Oak special meeting.

In addition, this document is a prospectus that is being delivered to Post Oak shareholders because Allegiance is offering shares of Allegiance common stock to Post Oak shareholders in connection with the merger.

This joint proxy statement/prospectus contains important information about the merger, the proposals being voted on at the Allegiance and Post Oak special meetings and important information to consider in connection with an investment in Allegiance common stock. You should read it carefully and in its entirety. The enclosed materials allow you to have your shares of common stock voted by proxy without attending your company’s special meeting. Your vote is important, and Allegiance and Post Oak encourage you to submit your proxy as soon as possible.

Completion of the merger is not conditioned upon approval of the Allegiance Charter Amendment Proposal or the Allegiance Adjournment Proposal.

The aggregate merger consideration that Post Oak shareholders would be entitled to receive in the merger will be reduced on a dollar-for-dollar basis (using the volume-weighted average price of Allegiance

common stock on the NASDAQ Stock Market, Inc. Global Market System (which we refer to as “NASDAQ”), for the twenty trading-day period ending on and including the fifth trading day before the day of completion of the merger (which we refer to as the “average closing price”) to determine the number of shares to be subtracted from the aggregate merger consideration) to the extent by which Post Oak’s tangible common equity, as defined in the merger agreement, is less than the minimum equity required by the merger agreement. The minimum equity required by the merger agreement is set at approximately $154.3 million if closing were to occur on the last business day of October 2018, and increases by $1.8 million for each month after October (and decreases by $1.8 million for each month prior to October). As of the date of this joint proxy statement/prospectus, Post Oak estimates that, assuming closing occurs on the last business day of October 2018, the Post Oak tangible common equity as of the closing of the merger will be $154.3 million or greater, resulting in no downward adjustment to the aggregate merger consideration with respect to the Post Oak tangible common equity.

For a discussion of the possible downward adjustment to the aggregate merger consideration including Post Oak’s estimates of its tangible common equity, see “The Merger Agreement—Structure of the Merger—Adjustments to Merger Consideration” beginning on page 113.

In addition, if the average closing price of Allegiance common stock is less than $32.52 per share and Allegiance common stock underperforms a selected index of public Texas community bank stocks by more than 20.0%, Post Oak has the right to terminate the merger agreement. Allegiance has the discretion, but not the obligation, to increase the merger consideration by increasing the number of shares of Allegiance common stock in the aggregate merger consideration such that the value of the aggregate merger consideration is equal to at least $278,564,572 (valuing the aggregate stock consideration based on the average closing price in accordance with the merger agreement). As a result, the number of shares of Allegiance common stock that Post Oak shareholders will receive in the merger may fluctuate with the market price of Allegiance common stock and will not be known at the time that Post Oak shareholders vote on the merger agreement.

Allegiance will not issue any fractional shares of Allegiance common stock in the merger. Post Oak shareholders who would otherwise be entitled to a fraction of a share of Allegiance common stock upon the completion of the merger will instead receive, for the fraction of a share, an amount in cash determined by multiplying the fractional share by the average closing price of Allegiance common stock.

As a result of the foregoing, based on the number of shares of Allegiance common stock and Post Oak common stock outstanding as of August 1, 2018, the last date before the date of this joint proxy statement/prospectus for which it was practicable to obtain this information, approximately 61.6% of outstanding Allegiance common stock following the merger will be held by shareholders who were holders of Allegiance common stock immediately prior to the effective time and approximately 38.4% of outstanding Allegiance common stock will be held by shareholders who were holders of Post Oak common stock immediately prior to the effective time.

The table below sets forth the implied value of the per share merger consideration based on the closing price of Allegiance common stock as quoted by NASDAQ on the specified dates:

The aggregate merger consideration that Post Oak shareholders would be entitled to receive in the merger will be reduced on a dollar-for-dollar basis (using the average closing price of Allegiance common stock to determine the number of shares to be subtracted from the aggregate merger consideration) to the extent by which Post Oak’s tangible common equity, as defined in the merger agreement, is less than the minimum equity required by the merger agreement. The minimum equity required by the merger agreement is set at approximately $154.3 million if closing were to occur on the last business day of October 2018, and increases by $1.8 million for each month after October (and decreases by $1.8 million for each month prior to October). For a discussion of the possible downward adjustment to the aggregate merger consideration including Post Oak’s estimates of its tangible common equity, see “The Merger Agreement—Structure of the Merger—Adjustments to Merger Consideration” beginning on page 113.

In addition, if the average closing price of Allegiance common stock is less than $32.52 per share and Allegiance common stock underperforms the selected index by more than 20.0%, Post Oak has the right to terminate the merger agreement. Allegiance has the discretion, but not the obligation, to increase the merger consideration by increasing the number of shares of Allegiance common stock in the aggregate merger consideration such that the value of the aggregate merger consideration is equal to at least $278,564,572 (valuing the aggregate stock consideration based on the average closing price in accordance with the merger agreement). As a result, the number of shares of Allegiance common stock that Post Oak shareholders will receive in the merger may fluctuate with the market price of Allegiance common stock and will not be known at the time that Post Oak shareholders vote on the merger agreement.

The Post Oak special meeting will be held at the corporate office of Post Oak at 2000 West Loop South, Suite 100, Houston, Texas 77027 on September 13, 2018, at 10:30 a.m. local time.

If you are a Post Oak shareholder and if your shares of Post Oak common stock are registered directly in your name, you are considered the shareholder of record with respect to those shares of Post Oak common stock. On the close of business on August 1, 2018, the record date for the Post Oak special meeting, Post Oak had approximately 907 holders of record.

If your shares of Allegiance common stock or Post Oak common stock are held in a stock brokerage account or by a bank or other nominee, the nominee is considered the record holder of those shares. You are considered the beneficial owner of these shares, and your shares are held in “street name.” This joint proxy statement/prospectus and the Allegiance proxy card or Post Oak proxy card, as applicable, have been forwarded to you by your nominee. As the beneficial owner, you have the right to direct your nominee concerning how to vote your shares by using the voting instructions it included in the mailing or by following its instructions for voting.

If you are an Allegiance shareholder, your broker does not have discretionary authority to vote your shares with respect to the Allegiance Merger Proposal, the Allegiance Stock Issuance Proposal, the Allegiance Charter Amendment Proposal or the Allegiance Adjournment Proposal. If you wish for the vote of your shares to be counted, you must direct your broker how to vote your shares.

If you are a Post Oak shareholder, your broker does not have discretionary authority to vote your shares with respect to the Post Oak Merger Proposal or the Post Oak Adjournment Proposal. If you wish for the vote of your shares to be counted, you must direct your broker how to vote your shares.

Abstentions and broker non-votes by Allegiance shareholders will not have the effect of a vote against the Allegiance Stock Issuance Proposal.

Abstentions and broker non-votes will have the effect of a vote against the Allegiance Merger Proposal, the Allegiance Charter Amendment Proposal and the Post Oak Merger Proposal because Texas law requires these proposals to be approved by the affirmative vote of the holders of two-thirds of the outstanding shares entitled to vote.

Abstentions and broker non-votes will not have the effect of a vote against the Allegiance Adjournment Proposal or the Post Oak Adjournment Proposal.

Allegiance Stock Issuance Proposal: The affirmative vote of a majority of the votes cast on the proposal at the Allegiance special meeting, in person or by proxy, is required to approve the Allegiance Stock Issuance Proposal. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or vote in person at the Allegiance special meeting or fail to instruct your bank or broker how to vote with respect to the Allegiance Stock Issuance Proposal, it will have no effect on the proposal.

Allegiance Charter Amendment Proposal: The affirmative vote of two-thirds of the outstanding shares of Allegiance common stock is required to approve the Allegiance Charter Amendment Proposal. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or vote in person at the Allegiance special meeting or fail to instruct your bank or broker how to vote with respect to the Allegiance Charter Amendment Proposal, it will have the effect of a vote AGAINST the proposal.

Allegiance Adjournment Proposal: The affirmative vote of a majority of the votes cast on the proposal at the Allegiance special meeting, in person or by proxy, is required to approve the Allegiance Adjournment Proposal. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or vote in person at the Allegiance special meeting or fail to instruct your bank or broker how to vote with respect to the Allegiance Adjournment Proposal, it will have no effect on the proposal.

Post Oak Adjournment Proposal: The affirmative vote of a majority of the votes cast on the proposal at the Post Oak special meeting, in person or by proxy, is required to approve the Post Oak Adjournment Proposal. If you mark “ABSTAIN” on your proxy card, fail to submit a proxy card or vote in person at the Post Oak special meeting or fail to instruct your bank or broker how to vote with respect to the Post Oak Adjournment Proposal, it will have no effect on the proposal.

Allegiance and Post Oak reserve the right to refuse admittance to anyone without proper proof of share ownership or without proper photo identification. The use of cameras, sound recording equipment, communications devices or any similar equipment during the special meetings is prohibited without Allegiance’s or Post Oak’s express written consent, respectively.

Holders of record and beneficial owners of Allegiance common stock can vote in person at the Allegiance special meeting. If you are a beneficial owner of Allegiance common stock, you must obtain a proxy card, executed in your favor, from the record holder of your shares, such as a broker, bank or other nominee, to be able to vote in person at the Allegiance special meeting.

Only Post Oak shareholders of record as of the Post Oak record date can vote in person at the Post Oak special meeting. If you are a beneficial owner of Post Oak common stock who holds shares in “street name” through a broker, bank, trustee or other nominee, you must direct your bank or broker how to vote in accordance with the instructions you have received from your bank or broker.

If you hold your shares of Allegiance common stock in “street name” through a bank or broker, you should contact your bank or broker to change your vote or revoke your proxy.

Post Oak shareholders: Yes. If you are a holder of record of Post Oak common stock, you may change your vote or revoke any proxy at any time before it is voted by (i) attending and voting in person at the Post Oak special meeting; (ii) giving notice of revocation of the proxy at the Post Oak special meeting; or (iii) delivering to the Secretary of Post Oak (A) a written notice of revocation or (B) a duly executed proxy card relating to the same shares, bearing a date later than the proxy card previously executed. Attendance at the Post Oak special meeting by itself will not automatically revoke your proxy. A revocation or later-dated proxy received by Post Oak after the vote will not be recognized and will not affect the vote. Post Oak’s Secretary’s mailing address is: 2000 West Loop South, Suite 100, Houston, Texas 77027.

If you hold your shares of Post Oak common stock in “street name” through a bank or broker, you should contact your bank or broker to change your vote or revoke your proxy.

For further information, please see “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 128. The U.S. federal income tax consequences described above may not apply to all holders of Post Oak common stock. Your tax consequences will depend on your individual situation. Accordingly, holders are urged to consult their own tax advisors for a full understanding of the particular tax consequences to them of the merger.

Post Oak shareholders: If you have any questions concerning the merger or this joint proxy statement/prospectus, would like additional copies of this joint proxy statement/prospectus or need help voting your shares of Post Oak common stock, please contact Renee Bourland, at (713) 439-3902 or renee.bourland@postoakbank.com.

SUMMARY

This summary highlights selected information from this joint proxy statement/prospectus. It may not contain all of the information that is important to you. Allegiance and Post Oak urge you to read carefully the entire joint proxy statement/prospectus, including the annexes, and the other documents to which they refer in order to fully understand the merger. A copy of the merger agreement is attached as Annex A. In addition, we incorporate by reference into this joint proxy statement/prospectus important business and financial information about Allegiance. See “Where You Can Find More Information” beginning on page 152. Each item in this summary refers to the page of this joint proxy statement/prospectus on which that subject is discussed in more detail.

Information about the Companies

Allegiance

Allegiance Bancshares, Inc. is a Texas corporation and registered bank holding company headquartered in Houston, Texas. Through its wholly-owned subsidiary, Allegiance Bank, Allegiance provides a diversified range of commercial banking services primarily to Houston metropolitan area-based small to medium-sized businesses, professionals and individual customers. Allegiance believes the size, growth and increasing economic diversity of the Houston metropolitan area, when combined with its super-community banking strategy, provides it with excellent opportunities for long-term, sustainable growth. Allegiance’s super-community banking strategy is designed to foster strong customer relationships while benefitting from a platform and scale that is competitive with larger regional and national banks. Allegiance believes this strategy presents a significant market advantage when serving small to medium-sized business customers and further enables Allegiance to attract talented bankers.

Allegiance currently operates 16 full-service banking locations and one loan production office in the Houston metropolitan area. Allegiance has experienced significant growth since it began banking operations in 2007, resulting from both organic growth, including de novo branching, and two whole-bank acquisitions. As of March 31, 2018, Allegiance had total assets of $2.89 billion, total gross loans of $2.29 billion, total deposits of $2.28 billion and total shareholders’ equity of $312.0 million.

Allegiance’s stock is traded on NASDAQ under the symbol “ABTX”.

Allegiance’s principal office is located at 8847 West Sam Houston Parkway, N., Suite 200, Houston, Texas 77040, and its telephone number at that location is (281) 894-3200. Additional information about Allegiance and its subsidiaries is included in documents incorporated by reference in this joint proxy statement/prospectus. See “Where You Can Find More Information,” beginning on page 152.

Post Oak

Formed in 2008, Post Oak is a Texas corporation that owns all of the outstanding shares of common stock of Post Oak Bank, N.A., a national banking association formed in 2004, with operational headquarters in Houston, Texas. Post Oak Bank is a traditional commercial bank offering a variety of banking services to commercial and consumer customers throughout the Houston metropolitan area and Beaumont, Texas. Post Oak Bank offers a range of lending services, including real estate, commercial and consumer loans to individuals and small- to medium-sized business and professional firms that are located in or conduct a substantial portion of their business in Post Oak Bank’s market areas.

Post Oak Bank operates 13 banking locations: 12 located throughout the greater Houston metropolitan area and one in Beaumont, outside of Houston. As of March 31, 2018, Post Oak, on a consolidated basis, reported total assets of $1.43 billion, total loans of $1.15 billion, total deposits of $1.24 billion and shareholders’ equity of $162.7 million. Post Oak does not file reports with the SEC because Post Oak is not a publicly-traded company.

Post Oak’s principal executive offices are located at 2000 West Loop South, Suite 100, Houston, Texas 77027, and its telephone number at that location is (713) 439-3900. Additional information about Post Oak and its subsidiaries is included in documents referred to in the section of this joint proxy statement/prospectus entitled “Where You Can Find More Information,” beginning on page 152.

In the Merger, Post Oak Shareholders Will Be Entitled To Receive Shares of Allegiance Common Stock

Merger Consideration

Allegiance and Post Oak are proposing a strategic merger. If the merger is completed, each share of Post Oak common stock (other than shares of Post Oak common stock held by Post Oak, Allegiance and any dissenting shareholder) will be converted into the right to receive 0.7017 of a share of Allegiance common stock. Allegiance will not issue any fractional shares of Allegiance common stock in the merger. Post Oak shareholders who would otherwise be entitled to a fraction of a share of Allegiance common stock upon the completion of the merger will instead receive, for the fraction of a share, an amount in cash determined by multiplying the fractional share by the average closing price of Allegiance common stock.

The Allegiance common stock is listed on NASDAQ under the symbol “ABTX.” See “Description of Capital Stock of Allegiance” for additional information about the Allegiance common stock. See “Comparison of Shareholders’ Rights” and “Comparative Market Prices and Dividends” for comparative information about the Allegiance common stock and the Post Oak common stock and the rights of holders thereof.

The market value of the shares of Allegiance common stock to be paid as consideration will fluctuate with the market price of Allegiance common stock and will not be known at the time the Post Oak shareholders vote on the Post Oak Merger Proposal and the Allegiance shareholders vote on the Allegiance Merger Proposal and the Allegiance Stock Issuance Proposal.

The table below sets forth the implied value of the per share merger consideration based on the closing price of Allegiance common stock as quoted by NASDAQ on the specified dates:

The merger agreement governs the merger. The merger agreement is included in this joint proxy statement/prospectus as Annex A. All descriptions in this summary and elsewhere in this joint proxy statement/prospectus of the terms and conditions of the merger are qualified by reference to the merger agreement. Please read the merger agreement carefully for a more complete understanding of the merger.

Adjustments to Merger Consideration

The aggregate merger consideration that Post Oak shareholders would be entitled to receive in the merger will be reduced on a dollar-for-dollar basis (using the average closing price of Allegiance common stock to determine the number of shares to be subtracted from the aggregate merger consideration) to the extent by which Post Oak’s tangible common equity, as defined in the merger agreement, is less than the minimum equity required by the merger agreement. The minimum equity required by the merger agreement is set at approximately $154.3 million if closing were to occur on the last business day of October 2018, and increases by $1.8 million for each month after October (and decreases by $1.8 million for each month prior to October). As of the date of this joint proxy statement/prospectus, Post Oak estimates that, assuming closing occurs on the last business day of October 2018, the Post Oak tangible common equity as of the closing of the merger will be $154.3 million or greater, resulting in no downward adjustment to the aggregate merger consideration with respect to the Post Oak tangible common equity. For additional information regarding the composition and determination of Post Oak tangible common equity, see “The Merger Agreement—Structure of the Merger—Adjustments to Merger Consideration” beginning on page 113.

In addition, if (1) the average closing price of the Allegiance common stock is less than $32.52 and (2) the number obtained by dividing the average closing price by $40.65 is less than the number obtained by dividing (A) the Final Index Price by (B) the Initial Index Price and subtracting 0.20 from such quotient, then Post Oak may give notice of its intent to terminate the merger agreement, at which time Allegiance has the discretion, but not the obligation, to increase the merger consideration by increasing the number of shares of Allegiance common stock in the aggregate merger consideration such that the value of the aggregate merger consideration is equal to at least $278,564,572 (valuing the aggregate stock consideration based on the average closing price in accordance with the merger agreement). The Final Index Price, as such term is used herein, is the average of the daily closing value of the Index for the 20 consecutive trading days ending on and including the fifth trading day preceding the closing date. The Initial Index Price, as such term is used herein, is $42.75 (the closing value of the Index on the date immediately prior to the date of the merger agreement). The Index, as such term is used herein, means the financial institutions with the following trading symbols on an equal weighted basis: CBTX, FFIN, GNBC, GNTY, IBTX, IBOC, LTXB, PB, SBSI and VBTX. If Allegiance elects to increase the merger consideration, Post Oak will no longer have the right to terminate the merger agreement for these reasons. If Allegiance elects not to increase the merger consideration, Post Oak may terminate the merger agreement.

The Allegiance Board Unanimously Recommends that Allegiance Shareholders Vote “FOR” the Allegiance Merger Proposal, “FOR” the Allegiance Stock Issuance Proposal, “FOR” the Allegiance Charter Amendment Proposal and “FOR” the Allegiance Adjournment Proposal (page 52)

The Allegiance Board has determined that the merger, the merger agreement and the transactions contemplated by the merger agreement, including the issuance of the Allegiance common stock, are advisable and in the best interests of Allegiance and its shareholders and has unanimously approved the merger agreement. The Allegiance Board recommends that Allegiance shareholders vote “FOR” the Allegiance Merger Proposal, “FOR” the Allegiance Stock Issuance Proposal and “FOR” the Allegiance Adjournment Proposal. For the factors considered by the Allegiance Board in reaching its decision to approve the merger agreement, see “The Merger—Allegiance’s Reasons for the Merger; Recommendation of the Allegiance Board” beginning on page 96. The Allegiance Board has also determined that the amendment to the Amended and Restated Certificate of Formation of Allegiance to increase the number authorized shares of capital stock is advisable and in the best interests of Allegiance and its shareholders. The Allegiance Board recommends that Allegiance shareholders vote “FOR” the Allegiance Charter Amendment Proposal.

The Post Oak Board Unanimously Recommends that Post Oak Shareholders Vote “FOR” the Post Oak Merger Proposal and “FOR” the Post Oak Adjournment Proposal (page 51)

The Post Oak Board has determined that the merger, the merger agreement and the transactions contemplated by the merger agreement are advisable and in the best interests of Post Oak and its shareholders and has unanimously approved the merger agreement. The Post Oak Board unanimously recommends that Post Oak shareholders vote “FOR” the Post Oak Merger Proposal and “FOR” the Post Oak Adjournment Proposal. For the factors considered by the Post Oak Board in reaching its decision to approve the merger agreement, see “The Merger-Post Oak’s Reasons for the Merger; Recommendation of the Post Oak Board” beginning on page 84.

Post Oak Director Support Agreements and Post Oak Voting Agreement (page 126); Ownership of Directors, Executive Officers and Affiliates (pages 149 and 151)

In connection with entering into the merger agreement, each of the directors of Post Oak and Post Oak Bank who is not a party to an employment agreement has entered into a Director Support Agreement with Allegiance pursuant to which each has agreed to refrain from harming the goodwill of Allegiance, Post Oak or any of their respective subsidiaries and their respective customer, client and vendor relationships.

The directors and certain officers of Post Oak and Post Oak Bank have entered into a voting agreement with Allegiance, solely in their capacity as shareholders of Post Oak, pursuant to which they have agreed to vote in favor of the Post Oak Merger Proposal and in favor of any other matter required to be approved by the shareholders of Post Oak to facilitate the transactions contemplated by the merger agreement. As of the Post Oak record date, the Post Oak shareholders who are party to the voting agreement beneficially own and are entitled to vote in the aggregate approximately 28.9% of the outstanding shares of Post Oak common stock. For more information regarding the voting agreement, see “The Merger Agreement—Post Oak Director Support Agreements and Post Oak Voting Agreement” beginning on page 126.

As of the Post Oak record date, the directors and executive officers of Post Oak and their affiliates beneficially owned and were entitled to vote, in the aggregate, 3,038,559 shares of Post Oak common stock, representing approximately 25.6% of the shares of Post Oak common stock outstanding on that date. Post Oak currently expects that each of its executive officers will vote their shares of Post Oak common stock in favor of the Post Oak Merger Proposal and the Post Oak Adjournment Proposal. As of the Post Oak record date, Allegiance beneficially owned no shares of Post Oak common stock, and the directors and executive officers of Allegiance and their affiliates beneficially owned no shares of Post Oak common stock.

As of the Allegiance record date, the directors and executive officers of Allegiance and their affiliates beneficially owned and were entitled to vote approximately 1,648,807 shares of Allegiance common stock representing approximately 12.3% of the shares of Allegiance common stock outstanding on that date. Allegiance currently expects that each of its executive officers will vote their shares of Allegiance common stock in favor of the Allegiance Merger Proposal, the Allegiance Stock Issuance Proposal, the Allegiance Charter Amendment Proposal and the Allegiance Adjournment Proposal, although none of them has entered into any agreement obligating him or her to do so. As of the Allegiance record date, Post Oak beneficially owned no shares of Allegiance common stock, and the directors and executive officers of Post Oak and their affiliates beneficially owned, in the aggregate, 2,056 shares of Allegiance common stock or less than 1.0% of the outstanding Allegiance common stock.

Opinion of Post Oak’s Financial Advisor (page 86 and Annex D)

On April 30, 2018, Performance Trust Capital Partners, LLC (“Performance Trust”) rendered to the Post Oak Board its written opinion with respect to the fairness, from a financial point of view, to the holders of Post Oak common stock, as of April 30, 2018, of the per share merger consideration plus the assumption and conversion of Post Oak stock options pursuant to the merger agreement (which is defined in the opinion as the “Aggregate Merger Consideration”). Performance Trust’s opinion was directed to the Post Oak Board and only addressed the fairness, from a financial point of view, to the holders of Post Oak common stock of the Aggregate Merger Consideration and did not address any other aspect or implication of the merger. The references to Performance Trust’s opinion in this joint proxy statement/prospectus are qualified in their entirety by reference to the full text of Performance Trust’s written opinion, which is included as Annex D to this joint proxy statement/prospectus and Performance Trust’s opinion sets forth the procedures followed, assumptions made, qualifications and limitations on the review undertaken and other matters considered by Performance Trust in preparing its opinion. However, neither Performance Trust’s opinion, nor the summary of its opinion and the related analyses set forth in this joint proxy statement/prospectus is intended to be, and they do not constitute, advice or a recommendation to the Post Oak Board or any shareholder of Post Oak as to how to act or vote with respect to any matter relating to the merger agreement or otherwise. Performance Trust’s opinion was furnished for the use and benefit of the Post Oak Board (in its capacity as such) in connection with its evaluation of the merger and should not be construed as creating, and Performance Trust will not be deemed to have, any fiduciary duty to the Post Oak Board, Post Oak, any security holder or creditor of Post Oak or any other person, regardless of any prior or ongoing advice or relationships. See “The Merger—Opinion of Post Oak’s Financial Advisor” beginning on page 86.

Fairness Opinion to Allegiance’s Board of Directors (page 97 and Annex E)

On April 30, 2018, at the request of the Allegiance Board, representatives of Raymond James & Associates, Inc. (“Raymond James”) rendered its written opinion, dated April 30, 2018, that as of such date and based upon and subject to the qualifications, assumptions and other matters considered in connection with the preparation of its opinion, the exchange ratio in the merger pursuant to the merger agreement was fair, from a financial point of view, to Allegiance.

The full text of the written opinion of Raymond James, dated April 30, 2018, which sets forth, among other things, the various qualifications, assumptions and limitations on the scope of the review undertaken, is included in this joint proxy statement/prospectus as Annex E. Raymond James provided its opinion for the information and assistance of the Allegiance Board (solely in each director’s capacity as such) in connection with, and for purposes of, the Allegiance Board’s consideration of the merger, and its opinion only addresses whether the exchange ratio was fair, from a financial point of view, to Allegiance as of the date of such opinion. The opinion of Raymond James did not address any other term or aspect of the merger agreement or the merger contemplated thereby. The Raymond James opinion does not constitute a recommendation to the Allegiance Board or any holder of Allegiance common stock or Post Oak common stock as to how the Allegiance Board, such shareholder or any other person should vote or otherwise act with respect to the merger or any other matter. See “The Merger—Opinion of Allegiance’s Financial Advisor” beginning on page 97.

How Post Oak Equity-Based Awards Will Be Treated (page 114)

Restricted Stock Awards

At the effective time, each restricted stock award granted by Post Oak will become fully vested and each holder of such restricted stock awards will be entitled to receive the per share merger consideration for each share of Post Oak common stock held by such holder.

Stock Options

Upon completion of the merger, each option to purchase shares of Post Oak common stock granted under the Post Oak Bancshares, Inc. Stock Option Plan, as amended, that is outstanding immediately prior to the merger will automatically be converted into an option to purchase shares of Allegiance common stock. The number of shares of Allegiance common stock purchasable under the converted option, as well as the exercise price of these stock options, will be adjusted to reflect the exchange ratio, rounded to the nearest whole share. Each converted option will remain subject to the same terms and conditions as were applicable prior to the merger.

Post Oak Will Hold the Post Oak Special Meeting on September 13, 2018 (page 48)

The Post Oak special meeting will be held on September 13, 2018, at 10:30 a.m. local time, at the corporate office of Post Oak at 2000 West Loop South, Suite 100, Houston, Texas 77027. At the Post Oak special meeting, Post Oak shareholders will be asked to approve the Post Oak Merger Proposal and the Post Oak Adjournment Proposal.

Only holders of record of Post Oak common stock at the close of business on August 1, 2018, the Post Oak record date, will be entitled to notice of and to vote at the Post Oak special meeting. Each share of Post Oak common stock is entitled to one vote on each proposal to be considered at the Post Oak special meeting. As of the Post Oak record date, there were 11,882,629 shares of Post Oak common stock entitled to vote at the Post Oak special meeting. As of the Post Oak record date, the directors and executive officers of Post Oak and their affiliates beneficially owned and were entitled to vote, in the aggregate, 3,038,559 shares of Post Oak common stock representing approximately 25.6% of the shares of Post Oak common stock outstanding on that date.

The Post Oak Merger Proposal will be approved if at least two-thirds of the outstanding shares of Post Oak common stock are voted in favor of such proposal. If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Post Oak special meeting or fail to instruct your bank or broker how to vote with respect to the Post Oak Merger Proposal, it will have the effect of a vote AGAINST the Post Oak Merger Proposal.

The Post Oak Adjournment Proposal will be approved if a majority of the votes cast on the proposal at the Post Oak special meeting are voted in favor of the proposal. If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Post Oak special meeting or fail to instruct your bank or broker how to vote with respect to the Post Oak Adjournment Proposal, it will have no effect on the proposal.

Allegiance Will Hold the Allegiance Special Meeting on September 14, 2018 (page 52)

The Allegiance special meeting will be held on September 14, 2018, at 1:00 p.m. local time, at The Houstonian Hotel at 111 North Post Oak Lane, Houston, Texas 77024. At the Allegiance special meeting, Allegiance shareholders will be asked to approve the Allegiance Merger Proposal, the Allegiance Stock Issuance Proposal, the Allegiance Charter Amendment Proposal and the Allegiance Adjournment Proposal.

Only holders of record of Allegiance common stock at the close of business on August 1, 2018, the Allegiance record date, will be entitled to notice of and to vote at the Allegiance special meeting. Each share of Allegiance common stock is entitled to one vote on each proposal to be considered at the Allegiance special meeting. As of the Allegiance record date, there were 13,367,590 shares of Allegiance common stock entitled to vote at the Allegiance special meeting. As of the Allegiance record date, the directors and executive officers of Allegiance and their affiliates beneficially owned and were entitled to vote approximately 1,648,807 shares of Allegiance common stock representing approximately 12.3% of the shares of Allegiance common stock outstanding on that date.

Each of the Allegiance Merger Proposal and the Allegiance Charter Amendment Proposal will be approved if at least two-thirds of the outstanding shares of Allegiance common stock are voted in favor of such proposal. If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Allegiance special meeting or fail to instruct your bank or broker how to vote with respect to the Allegiance Merger Proposal or the Allegiance Charter Amendment Proposal, it will have the effect of a vote AGAINST the Allegiance Merger Proposal and the Allegiance Charter Amendment Proposal.

Each of the Allegiance Stock Issuance Proposal and the Allegiance Adjournment Proposal will be approved if a majority of the votes cast at the Allegiance special meeting are voted in favor of each such proposal. If you mark “ABSTAIN” on your proxy, fail to submit a proxy or vote in person at the Allegiance special meeting or fail to instruct your bank or broker how to vote with respect to either of the Allegiance Stock Issuance Proposal or the Allegiance Adjournment Proposal, it will have no effect on such proposal.

Material U.S. Federal Income Tax Consequences of the Merger (page 128)

The obligations of Allegiance and Post Oak to complete the merger are conditioned on, among other things, the receipt by Allegiance and Post Oak of tax opinions from Bracewell and Fenimore Kay, respectively, dated as of the closing date of the merger, to the effect that, on the basis of facts, representations and assumptions that are consistent with the facts existing at the effective time and as set forth and referred to in such opinions, the merger will qualify for U.S. federal income tax purposes as a “reorganization” within the meaning of Section 368(a) of the Code.

If the merger qualifies as a reorganization under Section 368(a) of the Code, holders of Post Oak common stock generally will not recognize any gain or loss for U.S. federal income tax purposes on the exchange of shares of Post Oak common stock for shares of Allegiance common stock, except with respect to any cash received in lieu of fractional shares of Allegiance common stock. If any of the tax opinion representations and assumptions are incorrect, incomplete or false or are violated, the validity of the opinions described above may be affected and the tax consequences of the merger could differ from those described in this joint proxy statement/prospectus.

For further information, please see “Material U.S. Federal Income Tax Consequences of the Merger” beginning on page 128. The U.S. federal income tax consequences described above may not apply to all holders of Post Oak common stock. Tax matters are complicated, and the tax consequences of the merger to a particular shareholder will depend in part on such shareholder’s individual circumstances. Accordingly, holders are urged to consult their own tax advisors for a full understanding of the particular tax consequences to them of the merger.

Interests of Post Oak’s Directors and Executive Officers in the Merger (page 105)

In considering the recommendation of the Post Oak Board with respect to the merger agreement, you should be aware that certain of Post Oak’s directors and executive officers may have interests in the merger that are different from, or in addition to, the interests of the Post Oak shareholders generally. Interests of directors and executive officers that may be different from or in addition to the interests of the Post Oak shareholders include:

The agreements with Mr. Williams and Ms. Bourland are for a term of three years after the effective date of the merger and entitle the named individual to receive a base annual salary, a minimum bonus paid quarterly during the three-year period and a restricted stock award of 8,591 and 5,164 shares, respectively, that will vest over two years, plus reimbursement of certain business expenses and participation in certain employee benefit programs. The agreements also contain non-competition and non-solicitation obligations for three years from the effective date of the merger. For the entire three-year term, the aggregate value of the employment agreements (excluding any stock awards and perquisites) for Mr. Williams and Ms. Bourland is $1.45 million and $750,000, respectively.

The agreements with Messrs. Parra and Phillips and Ms. Sandel are for a term of two years after the effective date of the merger and entitle the named individual to receive a base annual salary, a minimum bonus paid quarterly during the two-year period and a restricted stock award of 6,898, 5,738 and 5,057 shares, respectively, that will vest over four years, plus reimbursement of certain business expenses and participation in certain employee benefit programs. The agreements also contain non-competition and non-solicitation obligations for two years from the effective date of the merger. For the entire two-year term, the aggregate value of the employment agreements (excluding any stock awards and perquisites) for Messrs. Parra and Phillips and Ms. Sandel is $749,000, $657,500 and $582,750, respectively.

The employment agreements entitle each named individual, after termination of employment with Allegiance Bank for any reason other than for cause (as defined in the employment agreement) or as a result of death or disability, to receive payment of base salary and bonus for the remainder of the term of the agreement from Allegiance Bank.

These interests are discussed in more detail in the section of this joint proxy statement/prospectus entitled “The Merger—Interests of Post Oak’s Directors and Executive Officers in the Merger” beginning on page 105. The Post Oak Board was aware of these interests and considered them, among other matters, in approving the merger agreement.

Post Oak does not anticipate that any of the payments described above will impact the amount of the per share merger consideration payable to the Post Oak shareholders. However, the payments to be made with respect to the retention payments and for the “tail” insurance will be accounted for in determining the Post Oak tangible common equity, as more specifically described in the merger agreement, for purposes of determining whether there would be a downward adjustment to the aggregate merger consideration. For additional information on the potential downward adjustments to the aggregate merger consideration, please see “The Merger Agreement—Structure of the Merger—Adjustments to Merger Consideration” beginning on page 113.

In addition, Charles Carmouche, a Post Oak director, is the beneficial owner of 2,056 shares, or less than 1.0%, of Allegiance common stock as of August 1, 2018. Mr. Carmouche disclosed such ownership at the meeting of the Post Oak Board at which the Post Oak Board approved the merger agreement and the transactions contemplated thereby.

Post Oak Shareholders Are Entitled to Assert Dissenters’ Rights (page 108 and Annex F)

Post Oak shareholders have the right to dissent from the merger and obtain payment in cash of the fair value of their shares of Post Oak common stock under the TBOC. In order for such Post Oak shareholder to perfect such Post Oak shareholder’s right to dissent, such Post Oak shareholder must carefully follow the procedure set forth in the applicable provisions of the TBOC. A copy of the applicable statutory provisions of the TBOC is included as Annex F to this joint proxy statement/prospectus and a summary of the provisions can be found under the section of this joint proxy statement/prospectus entitled “The Merger—Dissenters’ Rights of Post Oak Shareholders” beginning on page 108.

Conditions that Must Be Satisfied or Waived for the Merger to Occur (page 121)

Currently, Post Oak and Allegiance expect to complete the merger in the fourth quarter of 2018. As more fully described in this joint proxy statement/prospectus and in the merger agreement, the completion of the merger depends on a number of conditions being satisfied or, where legally permissible, waived. Allegiance’s and Post Oak’s respective obligations to complete the merger are subject to the satisfaction or waiver of the following conditions:

In addition to the conditions listed above, Post Oak’s obligation to complete the merger is subject to certain consents identified in the merger agreement having been obtained by Allegiance, and Post Oak having received evidence thereof in form and substance satisfactory to it.

In addition to the conditions listed above, Allegiance’s obligation to complete the merger is subject to the satisfaction of the following conditions:

Neither Post Oak nor Allegiance can provide assurance as to when or if all of the conditions to the merger can or will be satisfied or waived by the appropriate party, or that the merger will be completed.

Termination of the Merger Agreement (page 124)

Allegiance and Post Oak can mutually agree at any time to terminate the merger agreement without completing the merger. In addition, either Allegiance or Post Oak may decide, without the consent of the other, to terminate the merger agreement if:

Post Oak may terminate the merger agreement, without the consent of Allegiance, if the board of directors of Post Oak receives an unsolicited, bona fide alternative acquisition proposal (as defined in the merger agreement) and, under certain terms and conditions, determines that it is a superior proposal to that of the merger agreement and that the failure to accept such proposal would be inconsistent with its fiduciary duties; but, Allegiance has the right to adjust the terms and conditions of the merger agreement so that the superior proposal no longer constitutes a superior proposal.

Post Oak may also terminate the merger agreement if (1) the average closing price of the Allegiance common stock is less than $32.52 and (2) the number obtained by dividing the average closing price by $40.65 is less than the number obtained by dividing (A) the Final Index Price by (B) the Initial Index Price and subtracting 0.20 from such quotient. Upon receipt of such notice, Allegiance has the discretion, but not the obligation, to increase the merger consideration by increasing the number of shares of Allegiance common stock in the aggregate merger consideration such that the value of the aggregate merger consideration is equal to at least

$278,564,572 (valuing the aggregate stock consideration based on the average closing price in accordance with the merger agreement). The Final Index Price, as such term is used herein, is the average of the daily closing value of the Index for the 20 consecutive trading days ending on and including the fifth trading day preceding the closing date. The Initial Index Price, as such term is used herein, is $42.75 (the closing value of the Index on the date immediately prior to the date of the merger agreement). The Index, as such term is used herein, means the financial institutions with the following trading symbols on an equal weighted basis: CBTX, FFIN, GNBC, GNTY, IBTX, IBOC, LTXB, PB, SBSI and VBTX. If Allegiance elects to increase the merger consideration, Post Oak will no longer have the right to terminate the merger agreement for these reasons.

In addition, Allegiance may terminate the merger agreement, without the consent of Post Oak, if:

Termination Fee (page 125)

If the merger agreement is terminated under certain circumstances, including circumstances involving an alternative acquisition proposal and changes in the recommendation of the Post Oak Board, Post Oak may be required to pay to Allegiance a termination fee equal to $14.272 million or up to $775,000 for its merger-related expenses. This termination fee could discourage other companies from seeking to acquire or merge with Post Oak. Termination fees are discussed in more detail in the section of this joint proxy statement/prospectus entitled “The Merger Agreement—Termination Fee” beginning on page 125.

Regulatory Approvals Required for the Merger (page 111)

The merger cannot be completed unless it is approved by the Board of Governors of the Federal Reserve System (which we refer to as the “Federal Reserve”) or such approval is waived by the Federal Reserve. On June 14, 2018, Allegiance filed the required documentation with the Federal Reserve Bank of Dallas to request a waiver of its approval, which was granted on June 26, 2018.

In addition, the merger of Post Oak Bank with and into Allegiance Bank requires the approval of the Federal Deposit Insurance Corporation (which we refer to as the “FDIC”) and the Texas Department of Banking (which we refer to as the “TDB”).

On May 25, 2018, Allegiance Bank filed applications with the FDIC and the TDB to obtain approval of the bank merger. The U.S. Department of Justice will have between 15 and 30 days following approval by the FDIC to challenge the approval on antitrust grounds. While Post Oak and Allegiance do not know of any reason that the Department of Justice would challenge regulatory approval by the FDIC and believe that the likelihood of such action is remote, there can be no assurance that the Department of Justice will not initiate such a proceeding, or if such a proceeding is initiated, as to the result of any such challenge.

Although neither Post Oak nor Allegiance knows of any reason why it cannot obtain these regulatory approvals in a timely manner, Post Oak and Allegiance cannot be certain when or if they will be obtained.

The Rights of Post Oak Shareholders Will Change as a Result of the Merger (page 135)

The rights of Post Oak shareholders will change as a result of the merger due to differences in Allegiance’s and Post Oak’s governing documents. See “Comparison of Shareholders’ Rights” beginning on page 135 for a description of the material differences in shareholders’ rights under each of the Allegiance and Post Oak governing documents.

Market Prices of Securities; Dividends (page 146)

Shares of Allegiance common stock are traded on NASDAQ under the ticker symbol “ABTX.” The last reported sale price of Allegiance common stock on April 27, 2018, the last trading day before public announcement of the merger agreement, was $40.80 per share. The last reported sale price of Allegiance common stock on August 1, 2018 was $44.85 per share. There is no established public trading market for the shares of Post Oak common stock. Neither Allegiance nor Post Oak has historically paid dividends. See “Comparison of Market Prices and Dividends” for more information.

Risk Factors (page 38)

You should consider all the information contained in this joint proxy statement/prospectus in deciding how to vote for the proposals presented in this joint proxy statement/prospectus. In particular, you should consider the factors described under the section of this joint proxy statement/prospectus entitled “Risk Factors” beginning on page 38.

Recent Developments

On July 26, 2018, Allegiance announced its results of operations for the three and six months ended June 30, 2018. Allegiance reported net income of $7.6 million, or $0.55 per diluted share, for the three months ended June 30, 2018, and $15.3 million, or $1.12 per diluted share, for the six months ended June 30, 2018. Net interest income was $27.8 million and $54.7 million for three and six months ended June 30, 2018, respectively, and the net interest margin was 4.21% and 4.20% for the three and six months ended June 30, 2018, respectively. The yield on interest-earning assets was 5.12% and 5.07% for the three and six months ended June 30, 2018, respectively. Total noninterest expense was $19.9 million and $38.6 million for the three and six months ended June 30, 2018, respectively. Allegiance recorded a provision for loan losses of $631 thousand and $1.3 million for the three and six months ended June 30, 2018, respectively. At June 30, 2018, the allowance for loan losses totaled $23.8 million and total nonperforming assets were $14.6 million. Allegiance’s nonperforming assets to total assets ratio was 0.49% at June 30, 2018. At June 30, 2018, Allegiance reported total loans of $2.36 billion, total assets of $2.97 billion, total deposits of $2.31 billion, total interest-bearing deposits of $1.56 billion, total liabilities of $2.65 billion and shareholders’ equity of $319.9 million. At June 30, 2018, Allegiance’s estimated tier 1 common equity to risk-weighted assets ratio was 10.97% and its book value was $23.98 per share.

SELECTED CONSOLIDATED HISTORICAL FINANCIAL DATA OF ALLEGIANCE

The following selected consolidated historical financial data of Allegiance as of and for the three months ended March 31, 2018 and 2017, have been derived from Allegiance’s unaudited consolidated financial statements incorporated by reference into this joint proxy statement/prospectus. The following selected consolidated historical financial data of Allegiance as of December 31, 2017 and 2016 and for each of the years ended December 31, 2017, 2016 and 2015, have been derived from Allegiance’s audited consolidated financial statements incorporated by reference into this joint proxy statement/prospectus, and the selected consolidated historical financial data as of December 31, 2015, 2014 and 2013 and for the years ended December 31, 2014 and 2013, have been derived from Allegiance’s audited consolidated financial statements not included or incorporated by reference into this joint proxy statement/prospectus. Allegiance’s unaudited consolidated financial statements have been prepared on a basis consistent with Allegiance’s audited consolidated financial statements. In the opinion of management of Allegiance, such unaudited consolidated financial data as of and for the three months ended March 31, 2018 and 2017 reflect all adjustments, consisting only of normal and recurring adjustments, necessary for a fair presentation of the results for those periods. Allegiance’s historical results are not necessarily indicative of the results that may be expected for any future period. See “Where You Can Find More Information” beginning on page 152.

(10) Interim periods annualized.

SELECTED CONSOLIDATED HISTORICAL FINANCIAL DATA OF POST OAK

The following selected consolidated historical financial data of Post Oak as of and for the three months ended March 31, 2018 and 2017, have been derived from Post Oak’s unaudited consolidated financial statements included elsewhere in this joint proxy statement/prospectus. The following selected consolidated historical financial data of Post Oak as of and for each of the years ended December 31, 2017 and 2016, have been derived from Post Oak’s audited consolidated financial statements included elsewhere in this joint proxy statement/prospectus, and the selected consolidated historical financial data as of and for each of the years ended December 31, 2015, 2014 and 2013, have been derived from Post Oak’s audited consolidated financial statements not included or incorporated by reference into this joint proxy statement/prospectus. Post Oak’s historical results are not necessarily indicative of the results that may be expected for any future period. See “Where You Can Find More Information” beginning on page 152.

SELECTED UNAUDITED PRO FORMA FINANCIAL DATA

The following table shows selected unaudited pro forma combined consolidated financial information about the financial condition and results of operations of Allegiance giving effect to the merger. The selected unaudited pro forma combined consolidated financial information assumes that the merger is accounted for under the acquisition method of accounting. Under the acquisition method of accounting, the assets and liabilities of Post Oak, as of the effective date of the merger, will be recorded by Allegiance at their respective fair values and the excess of the merger consideration over the fair value of Post Oak’s net assets will be allocated to goodwill.

The table sets forth the information as if the merger had become effective on March 31, 2018, with respect to financial condition data, and on January 1, 2017, with respect to the results of operations data. The selected unaudited pro forma combined consolidated financial data has been derived from and should be read in connection with the unaudited pro forma combined consolidated financial information, including the notes thereto, which is included in this joint proxy statement/prospectus under “Unaudited Pro Forma Combined Consolidated Financial Statements.”

The selected unaudited pro forma combined consolidated financial information is presented for illustrative purposes only and does not necessarily indicate the financial results of the combined companies had the companies actually been combined at the beginning of the period presented. The selected unaudited pro forma combined consolidated financial information also does not consider any potential impacts of current market conditions on revenues, potential revenue enhancements, anticipated cost savings and expense efficiencies or asset dispositions, among other factors. Further, as explained in more detail in the notes accompanying the detailed unaudited pro forma combined consolidated financial information included under “Unaudited Pro Forma Combined Consolidated Financial Information,” the allocation of the purchase price reflected in the selected unaudited pro forma combined consolidated financial data is subject to adjustments and may vary from the actual purchase price allocation that will be recorded at the time the merger is completed. Additionally, the final adjustments may be different from the unaudited pro forma adjustments presented in this joint proxy statement/prospectus.

UNAUDITED PRO FORMA COMBINED CONSOLIDATED FINANCIAL STATEMENTS

The following unaudited pro forma combined consolidated balance sheet as of March 31, 2018, and the unaudited pro forma combined consolidated statements of income for the three months ended March 31, 2018, and the year ended December 31, 2017, have been prepared to show the impact on Allegiance’s historical financial position and results of operations of the consummation of the merger, including the expected issuance of 8,267,674 shares of Allegiance common stock to Post Oak’s shareholders based on 11,782,349 shares of Post Oak common stock outstanding at March 31, 2018.

The unaudited pro forma combined consolidated financial information and explanatory notes are based upon the following assumptions:

The unaudited pro forma combined consolidated financial statements give effect to the acquisition of Post Oak as a business combination under GAAP. Accordingly, all assets and liabilities were recorded at estimated fair value. Pro forma adjustments are included only to the extent they are (i) directly attributable to the acquisition, (ii) factually supportable and (iii) with respect to the unaudited pro forma combined statement of income, expected to have a continuing impact on the combined results. The pro forma adjustments are based on estimates made for the purpose of preparing these pro forma statements and are described in the accompanying notes. Allegiance’s management believes that the estimates used in these pro forma financial statements are reasonable under the circumstances.

The pro forma adjustments included herein are subject to change as additional information becomes available and additional analyses are performed. The final allocation of the purchase price will be determined after further valuation analyses under GAAP are performed with respect to the fair values of certain tangible and intangible assets and liabilities as of the date of acquisition. The final adjustments may be materially different from the unaudited pro forma adjustments presented herein. In addition, the pro forma financial statements do not include the effects of any potential cost savings which management believes will result from combining certain operating procedures.

Allegiance anticipates that the acquisition of Post Oak will provide the combined company with the ability to better serve its customers, reach new customers and reduce operating expenses. In addition, certain subjective estimates have been utilized in determining the pro forma adjustments applied to the historical results of operations of Post Oak. The pro forma information, while helpful in illustrating the financial characteristics of the combined company under one set of assumptions, does not reflect the benefits of expected cost savings or opportunities to earn additional revenue and, accordingly, does not attempt to predict or suggest future results. It also does not necessarily reflect what the historical results of the combined company would have been had Allegiance and Post Oak been combined during these periods.

The unaudited pro forma combined consolidated financial information has been derived from, and should be read in conjunction with, the historical consolidated financial statements and related notes of Allegiance and Post Oak.

UNAUDITED PRO FORMA CONSOLIDATED BALANCE SHEET

AS OF MARCH 31, 2018

UNAUDITED PRO FORMA CONSOLIDATED STATEMENTS OF INCOME

FOR THE THREE MONTHS ENDED MARCH 31, 2018