SUMMARY

        This summary highlights selected information from this proxy statement/prospectus and may not contain all of the information that is important to you. To understand the merger fully and for a more complete description of the legal terms of the merger, you should read carefully this entire proxy statement/prospectus, including the merger agreement and the other documents to which we have referred you. See "Where You Can Find More Information" beginning on page 133. Page references are included in this summary to direct you to a more complete description of the topics.

        Throughout this proxy statement/prospectus, "SDTB," refers to San Diego Trust Bank, "Pacific Premier" refers to Pacific Premier Bancorp, Inc. and the "Bank" refers to Pacific Premier Bank, Pacific Premier's banking subsidiary. Also, throughout this proxy statement/prospectus, the Agreement and Plan of Reorganization, dated as of March 5, 2013, among Pacific Premier, the Bank and SDTB, is referred to as the "merger agreement." The merger of SDTB with and into the Bank is referred to as the "merger."

Parties to the Proposed Merger (Page 92)

        Pacific Premier Bancorp, Inc.    Pacific Premier is a California-based bank holding company for the Bank, a California-chartered commercial bank. Pacific Premier's principal asset is all of the capital stock of the Bank. The Bank provides banking services to businesses, professionals and consumers in its primary market area of Southern California through ten locations in the cities of San Bernardino, Seal Beach, Huntington Beach, Los Alamitos, Irvine, Newport Beach, Palm Springs and Palm Desert, California. On March 15, 2013, the Bank completed its acquisition of First Associations Bank, or FAB, which added a new office in Dallas, Texas. The banking operations conducted in this new office will be exclusively focused on providing deposit and other services to homeowners associations, or HOAs, and HOA management companies nationwide, as discussed below. Through the Bank's branches and its Internet website at www.ppbi.com, the Bank offers a broad array of deposit and loan products and services for both businesses and consumer customers. As of December 31, 2012, Pacific Premier had, on a consolidated basis, total assets of $1.2 billion, total stockholders' equity of $134.5 million and total deposits of $904.8 million. At December 31, 2012, Pacific Premier had real estate loans and business loans collateralized by real estate totaling 67.9% of its gross loan portfolio. Beginning with the 2013 fiscal year, Pacific Premier's filing status with the Commission transitioned from a "smaller reporting company" to an "accelerated filer," as those terms are defined under Commission rules. Under the Commission's rules, Pacific Premier is permitted to continue to provide the scaled disclosure required of a "smaller reporting company" in its filings with the Commission until its quarterly report on Form 10-Q for the quarter ended March 31, 2013.

        Based on information contained in Schedule 13Ds, Schedule 13Gs and Schedule 13Fs filed with the Commission, there are two shareholders (each of which is an institutional shareholder) who collectively beneficially own an aggregate of approximately 14.81% of Pacific Premier's outstanding common stock. These two shareholders, together with the shares of Pacific Premier common stock beneficially owned by Steven Gardner, Pacific Premier's president and chief executive officer, beneficially own an aggregate of approximately 15.63% of Pacific Premier's outstanding common stock. Pacific Premier is not aware of any agreements, arrangements or understandings between such shareholders with respect to the voting or disposition of any shares of Pacific Premier common stock.

        Other than as publicly disclosed in their respective Schedule 13Ds, Schedule 13Gs or Schedule 13Fs filed with the Commission, Pacific Premier is not aware of any increase or decrease in the beneficial ownership of these seven shareholders, including as a result of the shares of common stock sold in Pacific Premier's recently completed public offering. To the extent that any of these seven shareholders purchased additional shares of Pacific Premier common stock in the offering or purchased or sold shares of Pacific Premier common stock in the open market, through privately negotiated

transactions or otherwise, their collective beneficial ownership of shares of Pacific Premier's common stock could have changed from the percentages provided above.

        Pacific Premier's principal executive offices are located at 17901 Von Karman Ave., Suite 1200, Irvine, California 92614 and its telephone number is (714) 431-4000.

Recent Developments Involving Pacific Premier

        On March 15, 2013, Pacific Premier completed its acquisition of FAB, which operated from its headquarters in Dallas, Texas. Prior to the acquisition, FAB was a commercial bank that exclusively focused on providing deposit and other services to HOAs and HOA management companies nationwide. FAB did not accept retail or consumer deposits or provide other lending or other more traditional banking services to consumers or other type of commercial customers. The FAB business of servicing HOAs and HOA management companies will be joined with the Bank's existing Premier Property Banking Unit, which focuses exclusively on generating business banking relationships and servicing the specialized banking needs of property management companies, HOA management companies and their respective clients. The provision of financial services to HOAs and HOA management companies is highly competitive. The Bank's Premier Property Banking Unit will be competing nationwide with a number of other financial institutions that provide banking services for property management, HOA management companies and HOAs.

        At December 31, 2012, FAB had total assets of approximately $375.7 million, total stockholders' equity of approximately $46.2 million and total deposits of approximately $319.8 million. As of December 31, 2012, Pacific Premier and FAB would have, on a pro forma consolidated basis, total assets of approximately $1.5 billion, total stockholders' equity of $147.4 million and total deposits of $1.2 billion. See "Unaudited Pro Forma Combined Consolidated Financial Data" beginning on page 114.

        San Diego Trust Bank.    SDTB is a California-chartered commercial bank that was founded by several of San Diego's most respected banking veterans and business leaders in 2003. SDTB operates three full-service banking offices located in San Diego, (one in the downtown area and one in the Point Loma area) and Encinitas, California. As of December 31, 2012, SDTB had total assets of $242.0 million, total stockholders' equity of $25.7 million and total deposits of $187.9 million.

        SDTB's principal executive offices are located at 2550 Fifth Avenue, Suite 1010, San Diego, California 92103 and its telephone number is (619) 525-1727.

The Merger (Page 41)

        The merger agreement is attached to this proxy statement/prospectus as Appendix A, which is incorporated by reference into this proxy statement/prospectus. Please read the entire merger agreement. It is the legal document that governs the merger. Pursuant to the terms and conditions set forth in the merger agreement, SDTB will be acquired by Pacific Premier whereby SDTB will merge with and into the Bank, with the Bank as the surviving institution. The parties expect to complete the merger late in the second quarter of 2013 or in the third quarter of 2013.

SDTB's Reasons for Merger and Factors Considered by SDTB's Board of Directors (Page 45)

        Based on SDTB's reasons for the merger described herein, including the fairness opinion of Keefe Bruyette & Woods, Inc., or KBW, an independent investment banking firm, the SDTB board of directors believes that the merger is fair to SDTB shareholders and in their best interests, and unanimously recommends that SDTB shareholders vote "FOR" approval of the merger agreement. For a discussion of the circumstances surrounding the merger and the factors considered by SDTB's board

of directors in approving the merger agreement, see "The Merger—SDTB's Reasons for the Merger" beginning on page 45.

Pacific Premier's Reasons for Merger (Page 47)

        As part of its business strategy, Pacific Premier evaluates opportunities to acquire bank holding companies, banks and other financial institutions. The acquisition of SDTB is consistent with this strategy and will result in the Bank expanding its operations into the new Southern California market of San Diego County. In addition to meeting one of its strategic objectives, Pacific Premier believes that the acquisition of SDTB will also (i) create new opportunities for the bank to provide its expansive products and services to the SDTB customers, (ii) improve and strengthen the Bank's deposit base with low cost core deposits and (iii) better position the Bank for long-term growth.

SDTB's Financial Advisor Believes that the Merger Consideration is Fair, From a Financial Point of View, to SDTB Shareholders (Page 47)

        KBW delivered its written opinion to SDTB's board of directors that, as of March 5, 2013, and based upon and subject to the factors and assumptions set forth in the opinion, the merger consideration to be received by the holders of the outstanding SDTB common stock pursuant to the merger agreement was fair from a financial point of view to such holders.

        The full text of the written opinion of KBW, dated March 5, 2013, which sets forth assumptions made, procedures followed, matters considered and limitations and qualifications on the review undertaken in connection with the opinion, is attached as Appendix B to this proxy statement/prospectus. SDTB's shareholders should read the opinion in its entirety. KBW provided its opinion for the information and assistance of SDTB's board of directors in connection with its consideration of the transaction. The KBW opinion does not address the underlying business decision to proceed with the merger and is not a recommendation as to how any holder of SDTB common stock should vote or make any election with respect to the merger agreement or any related matter.

        SDTB began working with KBW in April of 2012 for the primary purpose of identifying a potential strategic merger partner, which led to contacting Pacific Premier in September, 2012 and eventually entering into the merger agreement. SDTB engaged KBW as its exclusive financial advisor in November of 2012 and pursuant to the terms of KBW's engagement as financial advisor and other advisory services, SDTB agreed to pay KBW 1% of the aggregate consideration paid in an acquisition of SDTB plus $100,000 for a fairness opinion. As of the date of this proxy statement/prospectus, SDTB has paid $100,000 in fees to KBW in connection with the merger. SDTB estimates that the remaining fee payable to KBW in connection with the merger will be approximately $306,080.

SDTB Shareholders Will Receive Cash or Shares of Pacific Premier Common Stock for Each Share of SDTB Common Stock Exchanged in the Merger (Page 55)

        At the effective time of the merger, each outstanding share of SDTB common stock (subject to certain exceptions) will, by virtue of the merger and without any action on the part of a SDTB shareholder, be converted into the right to receive, subject to possible adjustment as discussed below, (i) $13.41 in cash, without interest, subject to downward adjustment as described below, or the per share cash consideration, or (ii) 1.114 shares of Pacific Premier common stock, subject to upward or downward adjustment based on changes in the stock price of Pacific Premier common stock as described below, or the per share stock consideration. Cash will be paid in lieu of any fractional share interest.

        SDTB shareholders will have the opportunity to elect the form of consideration to be received for all shares of SDTB common stock held by them, whether all stock, all cash or a combination of stock and cash, subject to the allocation procedures provided for in the merger agreement, which are intended to ensure that 50% of the aggregate value of the merger consideration is paid in the form of shares of Pacific Premier common stock, and 50% of the aggregate merger consideration is paid in cash.

        Per Share Cash Consideration and Possible Adjustment.    The cash portion of the merger consideration will be subject to downward adjustment if SDTB's aggregate transaction-related expenses exceed $3.0 million, on an after-tax equivalent basis, with any excess amount reducing the per share cash consideration by the quotient of (i) such excess amount divided by (ii) the total number of shares of issued and outstanding SDTB common stock. Pursuant to the terms of the merger agreement, SDTB's transaction-related expenses consist of certain fixed amounts, such as SDTB's accounting and advisory fees and expenses associated with the accrual of benefits, change in control and other contractual payments and non-competition payments payable to SDTB's Chairman, Chief Executive Officer and President, Michael E. Perry, which are estimated to amount to $2.8 million in the aggregate on an after-tax basis, of which $2.5 million is in connection with payments to Mr. Perry, as well as certain amounts that are not fixed, such as SDTB's legal fees and premiums for extended directors and officers liability insurance to the extent premiums exceed 200% of current SDTB premiums. As of April 1, 2013, which is the latest practicable date before the filing of this proxy statement/prospectus, the aggregate amount of estimated fixed transaction-related expenses plus the variable transaction-related expenses actually incurred by SDTB, on an after-tax equivalent basis, totaled approximately $2.9 million. Although no assurances can be made as to the final amount of SDTB's transaction-related expenses as of the closing date of the merger, SDTB does not anticipate that its transaction-related expenses, on an after-tax basis, will exceed $3.0 million based on currently available information. The cash portion of the merger consideration is not subject to an upward adjustment if SDTB's aggregate transaction-related expenses are less than $3.0 million, on an after-tax equivalent basis. Because the cash portion of the merger consideration is subject to a downward adjustment, the amount of cash consideration to be received will not be known at the time SDTB shareholders elect the form of merger consideration they wish to receive or when SDTB shareholders vote on the merger agreement. To the extent that no downward adjustment to the per share cash consideration occurs and based on the allocation procedures which will provide for 50% of the 2,151,395 shares of SDTB common stock outstanding shall elect to receive the per share cash consideration, the cash portion of the merger consideration would be $14,425,103, or $13.41 for each share of SDTB common stock.

        Per Share Stock Consideration and Possible Adjustment.    The per share stock consideration of 1.114 shares of Pacific Premier common stock is subject to possible downward or upward adjustment based on the average closing stock price of Pacific Premier common stock for the 10 trading day period ending on the fifth business day prior to the effective time of the merger, or the PPBI Average Share Price. If the PPBI Average Share Price is greater than $13.240, then the per share stock consideration will be adjusted downward to equal (i) $14.751 divided by (ii) the PPBI Average Share Price, rounded to the nearest thousandth. If the PPBI Average Share Price is less than $10.832, then the per share stock consideration will be adjusted upward to equal (x) $12.069 divided by (y) the PPBI Average Share Price, rounded to the nearest thousandth. In no event shall the upward adjustment to the per share stock consideration increase beyond a number of shares of Pacific Premier common stock that would result in Pacific Premier issuing to SDTB shareholders in the aggregate more than 19.9% of its outstanding shares of Pacific Premier common stock at the closing of the merger. Assuming a closing date immediately prior to the date of filing of this proxy statement/prospectus, the PPBI Average Share Price would be calculated to be $12.840, and therefore no adjustment would occur to the per share stock consideration. To the extent that no adjustment to the per share stock consideration occurs and based on the allocation procedures, which provide that 50% of the 2,151,395 shares of SDTB common stock outstanding shall receive the per share stock consideration, the stock portion of the merger consideration will result in 1,198,327 shares of Pacific Premier common stock being issued.

        Aggregate Merger Consideration.    The aggregate per share cash consideration together with the aggregate per share stock consideration is referred to as the merger consideration. Upon completion of the merger, approximately $30.0 million of merger consideration will be payable to the SDTB shareholders, or approximately $13.946 per share of SDTB common stock, which assumes (i) the per share cash consideration and the per share stock consideration are not adjusted, (ii) the implied value

of the per share stock consideration is $14.48 (based on the closing price per share of Pacific Premier's common stock on April 1, 2013) and (iii) that there are 2,151,395 shares of SDTB common stock outstanding.

        Merger Consideration Example.    The following table illustrates what the exchange ratio, the related per share stock consideration, the per share cash consideration and the aggregate stock, cash and merger consideration value, would be depending upon changes to the PPBI Average Share Price, ranging from 20% above $12.036, which was the PPBI Average Share Price as of March 5, 2013, to 20% below $ 12.036. The following table assumes there are 2,151,395 shares of SDTB common stock outstanding as of the closing date, and that the per share cash consideration is $13.41. The table reflects that the aggregate merger consideration paid will consist of 50% cash and 50% shares of Pacific Premier common stock, and therefore, 1,075,698 shares of SDTB common stock will be exchanged for the per share stock consideration. As described below under "The Merger—The Merger Consideration—Allocation Procedures" beginning on page 59, regardless of whether an SDTB shareholder makes an all-cash election or an all-stock election, that SDTB shareholder may nevertheless receive a mix of cash and shares of Pacific Premier common stock as merger consideration. The table does not reflect the fact that cash will be paid instead of fractional shares.

        The implied value of the per share stock consideration based on the exchange ratio continuing to be 1.114 shares of Pacific Premier common stock for one share of SDTB common stock on April 1, 2013 was $14.48, which amount was based on the closing price per share of Pacific Premier common stock on that date. The value of the stock portion of the merger consideration will (i) fluctuate based on the market price of Pacific Premier common stock and such value on the closing date of the merger and (ii) be subject to upward or downward adjustment if the PPBI Average Share Price is either less than $10.832 or greater than $13.240, and therefore, the value of the stock portion of the merger consideration will not be known at the time you vote on the merger agreement or elect the form of merger consideration you would like to receive. Pacific Premier's common stock is listed on the Nasdaq Global Market under the symbol "PPBI." You should obtain current market quotations for the Pacific Premier common stock.

        Upon completion of the merger, and based on 2,151,395 shares of SDTB common stock outstanding as of the date of this proxy statement/prospectus and assuming there is no adjustment to the per share stock consideration, SDTB shareholders are expected to receive 1,198,327 shares of

Pacific Premier common stock. Following the completion of the merger, and based on                        shares of Pacific Premier common stock outstanding as of March 28, 2013, the former SDTB shareholders will own approximately 7.20% of the outstanding shares of Pacific Premier common stock and the current shareholders of Pacific Premier will own the remaining approximately 92.80% of the outstanding shares of Pacific Premier common stock.

        The examples above are illustrative only and are based on the assumptions indicated. The value of the merger consideration that an SDTB shareholder actually receives will be based on the actual PPBI Average Share Price calculated prior to completion of the merger. The actual PPBI Average Share Price may be outside the range of the amounts set forth above, and as a result, the actual value of the merger consideration per share of SDTB common stock may not be shown in the above table.

        Fractional Shares.    No fractional shares of Pacific Premier common stock will be issued, and in lieu thereof, each holder of SDTB common stock who would otherwise be entitled to a fractional share interest will receive an amount in cash, without interest, determined by multiplying such fractional interest by $13.41, which amount reflects per share cash consideration, rounded to the nearest whole cent.

What Will Happen to Outstanding SDTB Stock Options (Page 60)

        Pursuant to the terms of the merger agreement, each stock option to purchase shares of SDTB's common stock, referred to in this proxy statement/prospectus as an SDTB option, that is outstanding but not exercisable will be declared fully vested and exercisable for a period of three (3) months ending immediately before the anticipated closing date of the merger. Each SDTB option that remains outstanding as of the closing of the merger will be cancelled in accordance with the San Diego Trust Bank Second Amended and Restated 2003 Stock Plan, referred to in this proxy statement/prospectus as the SDTB Stock Option Plan, upon the closing of the merger and each holder of such SDTB option will be entitled to receive from Pacific Premier, as soon as reasonably practicable after the effective time of the merger, but in no event later than three (3) days after such effective time, a single lump sum cash payment equal to the product of (i) the number of shares of SDTB common stock subject to such SDTB option immediately prior to the closing of the merger, and (ii) the excess, if any, of the per share cash consideration over the exercise price per share of such SDTB option, less any applicable taxes required to be withheld with respect to such payment. If the exercise price per share of any such SDTB option is equal to or greater than the per share cash consideration, such SDTB option will be canceled without any cash payment being made in respect thereof.

When and How to Choose the Method of Payment for Your Shares (Page 58)

        Shares of SDTB common stock will be exchanged for either shares of Pacific Premier common stock, cash or a combination of stock and cash, as chosen by you, subject to the election and allocation procedures discussed herein and described in detail in the merger agreement. A form for making an election will be sent to you under separate cover no later than the date that this proxy statement/prospectus is mailed to holders of record of SDTB common stock. The election form permits you:

•

to elect to receive shares of Pacific Premier common stock in exchange for all shares of SDTB common stock held by you, plus cash in lieu of any fractional share interest;



•

to elect to receive cash in exchange for all shares of SDTB common stock held by you;



•

to elect to receive shares of Pacific Premier common stock with respect to some of your shares of SDTB common stock and cash with respect to your remaining shares of SDTB common stock; or



•

to indicate that you make no election with respect to the merger consideration to be received by you in exchange for your shares of SDTB common stock.

        In order to make an effective election, you should complete the election form and return it as instructed with the stock certificates representing your shares of SDTB common stock. The election form must be received by the designated exchange agent by 5:00 p.m., Pacific Time approximately five business days prior to the closing date of the merger. After the election deadline you will not be able to change your election and you will be bound to the election you have made, subject to the allocation procedures described in this this proxy statement/prospectus.

        Your choice will be honored to the extent possible, but because of the overall limitation on the amount of cash and shares of Pacific Premier common stock available, whether you receive the amount of cash or stock you request will depend in part on how many other SDTB shareholders submit elections and how many choose to receive cash and how many choose to receive stock. Because 50% of the aggregate value of the merger consideration will paid in the form of shares of Pacific Premier common stock, and 50% of the aggregate merger consideration will be paid in cash, SDTB shareholders may not receive exactly the form of consideration that they elect and may receive a pro rata amount of cash and Pacific Premier common stock.

        Pacific Premier will not issue fractional shares. Instead, SDTB shareholders who receive Pacific Premier common stock will receive the value of any fractional share interest in cash, without interest, determined by multiplying such fractional interest by $13.41, which amount reflects the per share cash consideration, rounded to the nearest whole cent.

        After the election form and related transmittal materials have been received and processed and following the closing of the merger, you will be sent the cash and/or Pacific Premier common stock to which you are entitled. If you hold shares in street name, you will receive information from your broker or other holder of record advising you of the process for receiving the cash and/or Pacific Premier common stock to which you are entitled.

        You will need to surrender your SDTB common stock certificates to receive the appropriate merger consideration, but you should not send us any certificates now. You will receive detailed instructions on how to exchange your shares along with your election form and transmittal materials.

Per Share Market Price and Dividend Information (Page 88)

        Shares of Pacific Premier common stock currently trade on the Nasdaq Global Market under the symbol "PPBI." Shares of SDTB common stock are quoted on the OTC Market Group's OTCQB platform, which is the middle tier of the OTC Market Group, under the symbol "SDBK."

        The following table sets forth the closing sale prices of (i) Pacific Premier common stock as reported on the Nasdaq Stock Market, and (ii) SDTB common stock as quoted on the OTCQB, on March 5, 2013, the last trading-day before Pacific Premier announced the merger, and on                , 2013, the last practicable trading-day before the distribution of this proxy statement/prospectus. To help illustrate the market value of the per share stock consideration to be received by SDTB's shareholders, the following table also presents the equivalent market value per share of SDTB common stock as of March 5, 2013 and April 1, 2013, which were determined by multiplying the closing price for the Pacific Premier common stock on those dates by the exchange ratio of 1.114 of a share of Pacific Premier common stock for each share of SDTB common stock. The equivalent market value per share of SDTB common stock presented below does not reflect the possible upward or downward adjustment if the PPBI Average Share Price is either less than $10.832 or greater than $13.240, or the per share cash consideration that also will be received by holders of SDTB common stock. See "The Merger—The

Merger Consideration" beginning on page 55 for additional information about the merger consideration to be received by holders of SDTB common stock.

        The market price of Pacific Premier common stock and SDTB common stock will fluctuate prior to the date of the special meeting, the deadline for submitting your election regarding the merger consideration and the date you receive the merger consideration. SDTB shareholders should obtain a current price quotation for the shares of Pacific Premier common stock to update the implied value for a share of SDTB common stock.

        Pacific Premier has never declared or paid dividends on its common stock and does not anticipate declaring or paying any cash dividends in the foreseeable future. It is Pacific Premier's current policy to retain earnings to provide funds for use in its business.

        SDTB has not declared or paid any dividends to date during 2013. SDTB declared and paid a 3% stock dividend in each of April 2011 and April 2012, respectively. As a California-chartered bank, SDTB is subject to bank regulatory restrictions on payment of dividends. Pursuant to the merger agreement, SDTB has certain restrictions on the payment of dividends to its shareholders pending the closing of the merger. See "The Merger—Business Pending the Merger" beginning on page 65.

Material Federal Income Tax Consequences of the Merger (Page 78)

        The merger is intended to qualify as a "reorganization" within the meaning of Section 368(a) of the Internal Revenue Code of 1986, as amended, which is referred to in the proxy statement/prospectus as the Code, and it is a condition to completion of the merger that Pacific Premier and SDTB receive a legal opinion to that effect. If the merger is completed, the merger consideration that will be paid to the holders of SDTB common stock will include shares of Pacific Premier common stock (including cash for any fractional shares) and cash.

        Assuming the merger qualifies as a reorganization, subject to the limitations and more detailed discussion set forth in "The Merger—Material Federal Income Tax Consequences" of this proxy statement/prospectus, an SDTB shareholder that is a U.S. holder that receives solely shares of Pacific Premier common stock in exchange for all of its shares of SDTB common stock generally will not recognize gain or loss on such exchange, other than with respect to cash received in lieu of fractional shares of Pacific Premier common stock. An SDTB shareholder that is a U.S. Holder that receives solely cash in exchange for all of its shares of SDTB common stock generally will recognize gain or loss in connection with such exchange. An SDTB shareholder that receives shares of Pacific Premier common stock and cash in exchange for all of its shares of SDTB common stock generally will recognize gain (but not loss) on such exchange.

        Tax matters are complicated, and the tax consequences of the merger to a particular SDTB shareholder will depend in part on such shareholder's individual circumstances. Accordingly, you are urged to consult your own tax advisor for a full understanding of the tax consequences of the merger to you, including the applicability and effect of federal, state, local and foreign income and other tax laws.

Date, Time and Location of the Special Meeting (Page 37)

        The special meeting will be held at          .m., Pacific Time, on                , 2013, at                , California             . At the special meeting, SDTB shareholders will be asked to:

•

approve the merger agreement; and



•

approve a proposal to adjourn the special meeting if necessary to permit further solicitation of proxies if there are not sufficient votes at the time of the special meeting to approve the merger agreement.

Record Date and Voting Rights for the Special Meeting (Page 38)

        Each SDTB shareholder is entitled to vote at the special meeting if he or she owned shares of SDTB common stock as of the close of business on                , 2013. Each SDTB shareholder will have one vote at the special meeting for each share of SDTB common stock that he or she owned on that date.

        Shareholders of record may vote by mail, telephone, via the Internet or by attending the special meeting and voting in person. Each proxy returned to SDTB by a holder of SDTB common stock, which is not revoked, will be voted in accordance with the instructions indicated thereon. If no instructions are indicated on a signed proxy that is returned, such proxy will be voted "FOR" approval of the merger agreement and "FOR" the proposal to adjourn the special meeting if necessary to permit further solicitation of proxies on the proposal to approve the merger agreement.

Approval of the Merger Agreement Requires the Affirmative Vote of Holders of Majority of the Issued and Outstanding Shares of SDTB Common Stock (Page 39)

        The affirmative vote of the holders of a majority of the issued and outstanding shares of SDTB common stock is necessary to approve the merger agreement on behalf of SDTB. At the close of business on the record date, there were 2,151,395 shares of SDTB common stock outstanding held by 152 holders of record. Each holder of record of SDTB common stock on the record date is entitled to one vote for each share held on all matters to be voted upon at the special meeting. If a SDTB shareholder does not vote, it will have the same effect as a vote against the merger agreement.

        Holders of 518,866 shares of SDTB common stock, representing approximately 24.1% of the outstanding shares of SDTB common stock, have signed shareholder agreements with Pacific Premier agreeing to vote in favor of the merger agreement.

        Due to the structure of the merger and the number of shares of Pacific Premier common stock to be issued to SDTB shareholders pursuant to the merger agreement, Pacific Premier shareholders are not required by law or Pacific Premier's amended and restated certificate of incorporation and amended and restated bylaws to adopt the merger agreement or approve the merger or the issuance of the Pacific Premier common stock in connection with the merger.

Management of SDTB Owns Shares Which May Be Voted at the Special Meeting (Page 40)

        As of the record date, the executive officers and directors of SDTB, as a group, held 518,866 shares of SDTB common stock, or approximately 24.1% of the outstanding SDTB common stock and have each entered into shareholder agreements with Pacific Premier and SDTB pursuant to which they have agreed, among other things, in their capacity as shareholders of SDTB, to vote their shares of SDTB common stock in favor of the merger agreement. The form of shareholder agreement is attached as Annex A to the merger agreement, which is attached as Appendix A to this proxy statement/prospectus.

SDTB's Shareholders Have Dissenters' Rights (Page 85)

        Under the California General Corporation Law, or CGCL, holders of SDTB common stock have the right to demand appraisal of their shares of SDTB common stock in connection with the merger and to receive, in lieu of the merger consideration, payment in cash, for the fair value of their shares of SDTB common stock. Any shareholder electing to exercise dissenters' rights must not have voted his, her or its shares of SDTB common stock "FOR" approval of the merger agreement and must comply with the provisions of the CGCL in order to perfect its rights of dissent and appraisal. Strict compliance with the statutory procedures is required to perfect dissenters' rights. These procedures are described later in this proxy statement/prospectus, and a copy of the relevant provisions of California law is attached as Appendix C.

SDTB is Prohibited from Soliciting Other Offers (Page 68)

        SDTB has agreed that, while the merger is pending, it will not solicit, initiate, encourage or, subject to some limited exceptions, engage in discussions with any third party other than Pacific Premier regarding extraordinary transactions such as a merger, business combination or sale of a material amount of assets or capital stock.

Pacific Premier and SDTB Must Meet Several Conditions to Complete the Merger (Page 61)

        Completion of the merger depends on meeting a number of conditions, including the following:

•

shareholders of SDTB must approve the merger agreement;



•

Pacific Premier and SDTB must receive all required regulatory approvals for the merger, and any waiting periods required by law must have passed and no such approval may contain any condition that Pacific Premier's board of directors reasonably determines in good faith would materially reduce the benefits of the merger to such a degree that, had such condition been known, Pacific Premier would not have entered into the merger agreement;



•

there must be no law, injunction or order enacted or issued preventing completion of the merger;



•

the Pacific Premier common stock to be issued in the merger must have been approved for trading on the Nasdaq Global Market;



•

the representations and warranties of each of Pacific Premier and SDTB in the merger agreement must be true and correct, subject to the materiality standards provided in the merger agreement;



•

Pacific Premier and SDTB must have complied in all material respects with their respective obligations in the merger agreement;



•

each of the employment agreement entered into between the Bank and James T. Reschan, SDTB's Senior Executive Vice President and Chief Operating Officer, and the confidentiality, non-competition and non-solicitation agreement entered into between the Bank and Michael E. Perry, SDTB's Chairman, President and Chief Executive Officer, must not have been terminated and remain in full force and effect;



•

Pacific Premier and SDTB shall have received a written opinion that the merger will be treated for federal income tax purposes as a reorganization within the meaning of Section 368(a) of the Internal Revenue Code;



•

as of the closing date, SDTB's average total deposits during a specified period and Tier 1 capital must not be less than $171,000,000 and $21,200,000, respectively; and

•

dissenting shares must not represent 10% or more of the outstanding shares of SDTB common stock.

        Unless prohibited by law, either Pacific Premier or SDTB could elect to waive a condition that has not been satisfied and complete the merger anyway. The parties cannot be certain whether or when any of the conditions to the merger will be satisfied, or waived where permissible, or that the merger will be completed.

Pacific Premier and SDTB Have Filed Regulatory Applications to seek Regulatory Approvals to Complete the Merger (Page 64)

        To complete the merger, the parties need the prior approval of or waiver from the Board of Governors of the Federal Reserve System, or the Federal Reserve, and the California Department of Financial Institutions, or CA DFI. The U.S. Department of Justice is able to provide input into the approval process of federal banking agencies and will have between fifteen (15) and thirty (30) days following any approval of a federal banking agency to challenge the approval on antitrust grounds. Pacific Premier and SDTB have filed all necessary applications with the Federal Reserve and the CA DFI, and a waiver request from certain application requirements will be filed with the Federal Reserve. Pacific Premier and SDTB cannot predict whether the required regulatory approvals and waivers will be obtained or whether any such approvals or waivers will have conditions which would be detrimental to Pacific Premier following completion of the merger.

Pacific Premier, the Bank and SDTB may Terminate the Merger Agreement (Page 71)

        Pacific Premier, the Bank and SDTB can mutually agree at any time to terminate the merger agreement before completing the merger, even if shareholders of SDTB have already voted to approve it.

        Pacific Premier and the Bank on one hand or SDTB on the other hand can also terminate the merger agreement:

•

if the other party breaches any of its representations, warranties, covenants or agreements under the merger agreement that (i) cannot be or has not been cured within thirty (30) days of the giving of written notice to the breaching party or parties and (ii) would entitle the non-breaching party or parties not to consummate the merger;



•

if the merger is not consummated by September 30, 2013, except to the extent that the failure to consummate by that date is due to (i) the terminating party's failure to perform or observe its covenants and agreements in the merger agreement, or (ii) the failure of any of the SDTB shareholders (if SDTB is the party seeking to terminate) to perform or observe their respective covenants under the relevant shareholder agreement;



•

if any required governmental approval of the merger has been denied by final non-appealable action or an application for approval of the merger has been permanently withdrawn at the request of a governmental authority, provided that no party has the right to terminate the merger agreement if the denial is due to the terminating party's failure to perform or observe its covenants in the merger agreement; or



•

if the shareholders of SDTB do not approve the merger agreement.

        In addition, Pacific Premier may terminate the merger agreement at any time prior to the special meeting if the board of directors of SDTB withdraws or modifies its recommendation to the SDTB shareholders that the merger agreement be approved in any way which is adverse to Pacific Premier, or breaches its covenants requiring the calling and holding of a meeting of shareholders to consider the merger agreement and prohibiting the solicitation of other offers. Pacific Premier also may terminate

the merger agreement if a third party commences a tender offer or exchange offer for 15% or more of the outstanding SDTB common stock and the board of directors of SDTB recommends that SDTB shareholders tender their shares in the offer or otherwise fails to recommend that they reject the offer within a specified period.

Termination Fee (Page 71)

        SDTB must pay Pacific Premier a termination fee of $1.75 million if the merger agreement is terminated under specified circumstances.

Pacific Premier, the Bank and SDTB May Amend the Merger Agreement (Page 70)

        The parties may amend or supplement the merger agreement by written agreement at any time before the merger actually takes place; provided, however, no amendment may be made after the special meeting which by law requires further approval by the shareholders of SDTB without obtaining such approval.

SDTB's Directors and Officers Have Some Interests in the Merger that Are in Addition to or Different than Your Interests (Page 73)

        SDTB directors and officers have interests in the merger as individuals that are in addition to, or different from, their interests as shareholders of SDTB, which are:

•

a confidentiality, non-competition and non-solicitation agreement between the Bank and Michael E. Perry, who currently serves as SDTB's Chairman, President and Chief Executive Officer, which will become effective upon consummation of the merger and termination of Mr. Perry's employment, and pursuant to which Mr. Perry will agree not to serve any financial institution operating in San Diego County in any capacity for three (3) years in consideration for receiving a fee from the Bank payable in three (3) equal annual installments of $375,000, on a pre-tax basis with the first installment payable on the closing of the merger, and the remaining two (2) installments payable on the first and second anniversaries of the closing of the merger;



•

an employment agreement between the Bank and James T. Reschan, who currently serves as SDTB's Senior Executive Vice President and Chief Operating Officer, which will become effective upon consummation of the merger and pursuant to which Mr. Reschan will receive an annual base salary of $200,000;



•

SDTB's directors and executive officers will receive an aggregate amount of approximately $1,450,874 in connection with the cancellation of their SDTB options upon the consummation of the merger;



•

the agreement of Pacific Premier to honor indemnification obligations of SDTB for a period of six (6) years, as well as to purchase liability insurance for SDTB's directors and officers for three (3) years following the merger, subject to the terms of the merger agreement;



•

the agreement of Pacific Premier to assume SDTB's obligations under insurance-funded supplemental executive retirement plans with Mr. Perry, as well as receiving certain life insurance policies intended to fund these plans. As a result of the merger, Mr. Perry will begin to receive payments of $277,879 per year for ten years that he would otherwise have received if he retired at age 65 or older. At the end of that ten-year period he will receive five additional years of payments of $161,580 under a separate deferred compensation plan that, but for the merger, he would have received after retirement on or after age 65. At March 31, 2013, the life insurance policies to be received by Pacific Premier and intended to fund Mr. Perry's plans had an aggregate cash value of approximately $2,869,733 with death benefits of approximately $7,638,839 payable to SDTB;

•

aggregate payments over 18 months to Mr. Perry in the amount of $1,415,903, on a pre-tax basis, pursuant to the terms of his employment agreement with SDTB; and



•

payments to Mr. Perry upon the closing of the merger pursuant to other contractual arrangements with SDTB, the aggregate amount of which is equal to approximately $118,641, on a pre-tax basis.

        Upon the closing of the merger, pursuant to the terms of his confidentiality, non-competition and non-solicitation agreement with the Bank, as well as his employment agreement, SDTB stock options and other contractual arrangements with SDTB, Mr. Perry will be entitled to receive an aggregate of $3,266,592, on a pre-tax basis. In addition, Pacific Premier will assume SDTB's obligations under the Supplemental Executive Retirement Plans with Mr. Perry and Mr. Perry's deferred compensation agreement to pay Mr. Perry an aggregate amount of $3,586,690 over the next 15 years, for which Pacific Premier will accrue a liability upon the closing of the merger, in addition to SDTB's existing liability, in the amount of $1,648,151 on a pre-tax basis. The cash portion of the merger consideration will be subject to downward adjustment if SDTB's aggregate transaction-related expenses exceed $3.0 million, on an after-tax equivalent basis. Pursuant to the terms of the merger agreement, SDTB's transaction-related expenses consist of certain fixed amounts, such as SDTB's accounting and advisory fees and expenses associated with the accrual of benefits and payments payable to Mr. Perry described above, which are estimated to amount to $2.8 million in the aggregate on an after-tax basis, of which $2.5 million is associated with the accrual of benefits and payments payable to Mr. Perry described above. SDTB's transaction-related expenses also consist of certain amounts that are not fixed, such as SDTB's legal fees and premiums for extended directors' and officers' liability insurance to the extent premiums exceed 200% of current SDTB premiums. To the extent that the variable amounts cause SDTB's aggregate transaction-related expenses to exceed $3.0 million, on an after-tax equivalent basis, and the cash portion of the merger consideration is reduced by such excess, all of SDTB's transaction-related expenses, including the payments made to Mr. Perry, the liability accrued by Pacific Premier related to future payments to Mr. Perry and the premiums for extended directors' and officers' liability insurance, to the extent premiums exceed 200% of current SDTB premiums, will have the effect of reducing the merger consideration payable to SDTB's shareholders. The cash portion of the merger consideration is not subject to an upward adjustment if SDTB's aggregate transaction-related expenses are less than $3.0 million, on an after-tax equivalent basis. Although no assurances can be made as to the final amount of SDTB's aggregate transaction-related expenses, SDTB does not anticipate that its variable transaction-related expenses will cause its aggregate transaction-related expenses to exceed $3.0 million.

        The board of directors of SDTB was aware of the foregoing interests and considered them, among other matters, in approving the merger agreement and the merger.

Accounting Treatment of the Merger (Page 82)

        The merger will be accounted for under the purchase method of accounting under generally accepted accounting principles, or GAAP.

Shareholders of Pacific Premier and SDTB Have Different Rights (Page 124)

        The rights of shareholders of Pacific Premier differ from the rights of shareholders of SDTB. Pacific Premier is incorporated under the laws of the State of Delaware and SDTB is incorporated under the laws of the State of California. The rights of holders of Pacific Premier common stock are governed by the Delaware General Corporation Law, or DGCL, as well as its amended and restated certificate of incorporation and amended and restated bylaws, and the rights of holders of SDTB common stock are governed by the California Financial Code and the CGCL, as well as its articles of incorporation and bylaws. Shareholders of SDTB who will receive shares of Pacific Premier common stock in exchange for their shares of SDTB common stock and become shareholders of Pacific Premier and their rights as shareholders of Pacific Premier will be governed by Pacific Premier's amended and restated certificate of incorporation and amended and restated bylaws and the DGCL.

SELECTED HISTORICAL FINANCIAL DATA

        The following tables present selected consolidated historical financial data of Pacific Premier and selected historical financial data of SDTB.

Selected Consolidated Historical Financial Data of Pacific Premier

        Set forth below are selected historical financial data derived from Pacific Premier's audited consolidated financial statements as of and for the years ended December 31, 2012, 2011, 2010, 2009 and 2008. You should read the information set forth below together with Pacific Premier's consolidated financial statements and related notes included in Pacific Premier's Annual Report on Form 10-K for the year ended December 31, 2012, which was filed with the Commission on March 14, 2013 and is incorporated by reference in this proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 133.

        On March 15, 2013, Pacific Premier completed its acquisition of FAB, which operated from its headquarters in Dallas, Texas. In connection with the consummation of the FAB acquisition, Pacific Premier issued 1,279,217 shares of its common stock and $37.2 million in cash as consideration to the holders of FAB common stock in exchange for their shares. On December 11, 2012, Pacific Premier completed an underwritten public offering of 3.3 million shares of its common stock at a public offering price of $10.00 per share. The net proceeds from the offering after deducting underwriting discounts and commissions was $31.2 million. On January 9, 2013, Pacific Premier issued an additional 495,000 shares of its common stock at a public offering price of $10.00 per share in connection with the underwriters' exercise of the over-allotment option granted to them as part of the offering. The net proceeds from the over-allotment after deducting underwriting discounts and commissions was $4.7 million.

        The selected historical financial data in the table below does not reflect either (i) the acquisition of FAB on March 15, 2013 or the 1,279,217 shares of Pacific Premier common stock and $37.2 million in cash paid as consideration to the holders of FAB common stock in exchange for their FAB shares or (ii) the sale of the 495,000 shares of Pacific Premier common stock or the related net proceeds of $4.7 million received by Pacific Premier in January 2013 as a result of the underwriters' exercise of their over-allotment option. See "Summary—Selected Unaudited Pro Forma Combined Consolidated Financial Data" on page 24 and "Unaudited Pro Forma Combined Consolidated Financial Data" beginning on page 114.

Selected Historical Financial Data of SDTB

        Set forth below is selected historical financial data derived from SDTB's audited financial statements as of and for the years ended December 31, 2012 and 2011. SDTB shareholders should read this information in conjunction with the section of this proxy statement/prospectus entitled "Management's Discussion and Analysis of Financial Condition and Results of Operations of SDTB" beginning on page 96 and the audited financial statements of SDTB which appear in this proxy statement/prospectus following the "Index to SDTB Financial Statements" beginning on page F-1. The historical results presented in the following summary do not necessarily indicate expected results for future periods.