SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K/A

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported) January 17, 2014

CENTERSTATE BANKS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (863) 419-7750

Not Applicable

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

Explanatory Note

On January 17, 2014, CenterState Banks, Inc. (the “Company”, “CSFL” or “CenterState”) furnished a Current Report on Form 8-K to report the January 17, 2014 completion of its previously announced transaction as described in the Agreement and Plan of Merger dated July 29, 2013, as amended (the “Agreement”) with Gulfstream Bancshares, Inc. (“GS” or “Gulfstream”) whereby GS merged with and into the Company. Pursuant to and simultaneously with the merger of GS with and into the Company, GS’s wholly owned subsidiary bank, Gulfstream Business Bank (“GSB”), merged with and into the Company’s wholly owned subsidiary bank, CenterState Bank of Florida, N.A. (the “Bank”).

This Current Report on Form 8-K/A amends and supplements the disclosures provided in Item 2.01 and 9.01 of the Current Report on Form 8-K furnished on January 17, 2014. Except as otherwise provided herein, the other disclosures made in the Current Report furnished on January 17, 2014 remain unchanged. The Company does not anticipate that it will further amend this Current Report.

Statements made in this amendment, other than those concerning historical financial information, may be considered forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995 and are subject to risks and uncertainties. These forward-looking statements include, without limitation, statements regarding the Company’s expectations concerning its financial condition, operating results, cash flows, liquidity and capital resources, including the effects of the GS and GSB acquisitions and the final determination of the assets and liabilities acquired and their respective valuations. A discussion of risks, uncertainties and other factors that could cause actual results to differ materially from management’s expectations is set forth under the captions “Business—Note about Forward-Looking Statements,” “Risk Factors” and “Management’s Discussion and Analysis of Financial Condition and Results of Operations” in the Company’s Annual Report on Form 10-K for the year ended December 31, 2013.

On January 17, 2014 the Company completed its previously announced merger transaction as set forth in the Agreement with GS, whereby GS merged with and into the Company. Pursuant to and simultaneously with the merger of GS with and into the Company, GS’s wholly owned subsidiary bank, GSB merged with and into the Bank.

Pursuant to the terms of the Agreement, the Company purchased approximately $377.9 million of loans. The purchase price and estimated fair market value of the loans was approximately $359.6 million or 95% of their outstanding unpaid principal balance.

The Company acquired four banking offices from GS. Two banking offices were purchased at fair market value based on current appraisals, approximately $5.5 million, and the Company assumed the existing leases on two locations, which terms approximated current fair market values.

All of the deposits, approximately $478.2 million, were assumed by the Bank. The Company did not pay a premium for the deposits assumed.

The Company also assumed two trust preferred securities issued by GS, one for $7 million and another for $3 million, which qualify for Tier 1 capital. Interest payments are due quarterly at a rate of LIBOR plus 1.90% on the $7 million trust preferred security and a rate of LIBOR plus 1.70% on the $3 million trust preferred security. The instruments mature in 2035 and 2037, respectively.

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On February 14, 2014, the four purchased GSB branches were converted to the Company’s core processing system. The Bank hired substantially all of GSB’s loan officers and branch employees, releasing primarily back office and support staff. Approximately 62 former GSB employees, about 77% of GSB’s former work force, were hired by the Bank.

The Company expects to recognize goodwill on this acquisition of approximately $31.1 million. This Goodwill is calculated based on the fair values of the assets acquired and liabilities assumed as of the acquisition date. Fair value estimates are based on the information available, and are subject to change for up to one year after the closing date of the acquisition as additional information relative to closing date fair values becomes available. Fair values are preliminary estimates due to pending appraisals on loan and other real estate owned.

The foregoing summary is not complete and is qualified in its entirety by reference to the full text of the form of the Agreement, incorporated by reference to Exhibit 2.1 to the Company’s Registration Statement on Form S-4 (File No. 333-191536.

Discussion

As set forth in Item 2.01 above, on January 17, 2014, the Company acquired assets and assumed all of the deposits and other liabilities of GS and GSB pursuant to the Agreement. A narrative description of the anticipated effects of the GS acquisition (the “Acquisition”) on the Company’s financial condition, liquidity, capital resources and operating results is presented below. This discussion should be read in conjunction with the historical financial statements and the related notes of the Company, which have been filed with the Securities and Exchange Commission (the “Commission”) and the Audited Statements, which are attached hereto as Exhibits 99.1 and 99.2.

The Company’s primary reasons for the transaction included to further solidify its market share in the southeast Florida market and expand its customer base to enhance deposit fee income and leverage operating costs through economies of scale. The acquisition increased the Company’s total assets and total deposits by approximately 23% and 23%, respectively, as compared with the balances at December 31, 2013, and is expected to positively affect the Company’s operating results to the extent the Company earns more from interest earning assets than it pays in interest on its interest bearing liabilities. The ability of the Company to successfully collect interest and principal on the loans acquired will also impact cash flows and operating results.

The Company estimated the acquisition date fair value of the acquired assets and assumed liabilities in accordance with Financial Accounting Standards Board (“FASB”) Accounting Standards Codification (“ASC”) Topic 805, Business Combinations (ASC Topic 805) and ASC Topic 820, Fair Value Measurements. However, the amount that the Company realizes on these assets may differ materially from these carrying values primarily as a result of changes in the timing and amount of collections on the acquired loans in future periods.

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Calculation of Purchase Price

The Company acquired 100% of the outstanding common stock of Gulfstream. The purchase price consisted of both cash and stock. Each share of Gulfstream common stock was exchanged for $14.65 cash and 3.012 shares of the Company’s common stock. Based on the closing price of the Company’s common stock on January 16, 2014, the resulting purchase price was $82,040. The table below summarizes the purchase price calculation. Dollar amounts are in thousands, except per share data.

Financial Condition

The total purchase price as shown in the table above is allocated to Gulfstream’s tangible and intangible assets and liabilities as of January 17, 2014 based on fair values as follows. Amounts are in thousands of dollars.

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The list below summarizes the preliminary estimates of the fair value of the assets purchased, excluding goodwill, and liabilities assumed as of the January 17, 2014 purchase date. Amounts are in thousands of dollars.

In the acquisition, the Company purchased $359.6 million of loans at fair value, net of $18.3 million, or 4.8%, estimated discount to the outstanding principal balance, representing 24.4% of the Company’s total loans at December 31, 2013. Of the total loans acquired, management identified approximately $30.1 million of loans with credit deficiencies. All loans that were on non-accrual status and all loan relationships that were greater than $500,000 and identified as impaired as of the acquisition date were considered by CenterState’s management to be credit impaired and will be accounted for pursuant to ASC Topic 310-30. The table below summarizes the total contractually required principal and interest cash payments, management’s estimate of expected total cash payments and fair value of the loans as of January 17, 2014 for purchased credit impaired loans. Contractually required principal and interest payments have been adjusted for estimated prepayments. Amounts are in thousands of dollars.

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The table below presents information with respect to the fair value of acquired loans and other interest earning assets, as well as their unpaid principal balance (“Book Balance”) at acquisition date, contractual term and average contractual yield as of the January 17, 2014 acquisition date. Amounts are in thousands of dollars.

The difference between the fair value of the loans acquired and their related book balance will be accreted into interest income over the life of the related loan. The following table reflects the scheduled maturities of the acquired loans at January 17, 2014. Amounts are in thousands of dollars.

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In the acquisition, the Company assumed $479.0 million in deposits at estimated fair value. The amount represents approximately 23% of the Company’s total deposits of $2,056.2 million at December 31, 2013. Non-interest bearing deposits comprise about 37%, money market accounts comprise about 37%, and time deposits comprise about 17% of the assumed deposits. The remainder is in interest bearing accounts and regular savings accounts. A schedule of the deposits assumed at January 17, 2014 at fair value is listed in the table below. Amounts are in thousands of dollars.

The following table presents the amount of time deposits assumed at January 17, 2014, maturing during the periods reflected below. Amounts are in thousands of dollars.

In its assumption of the deposit liabilities, the Company believed that these deposits have an intangible value. The Company applied ASC Topic 805, which prescribes the accounting for goodwill and other intangible assets such as core deposit intangibles, in a business combination. The Company determined the estimated fair value of the core deposit intangible asset totaled $4.2 million, which will be amortized utilizing an accelerated amortization method over an estimated economic life not to exceed ten years. In determining the valuation amount, deposits were analyzed based on factors such as type of deposit, deposit retention, interest rates and age of deposit relationships. The table below presents the estimated amortization expense for each of the next ten years. Amounts are in thousands of dollars.

Future amortization of this core deposit intangible asset over the estimated life will decrease results of operations, net of any potential tax effect. Since amortization is a non cash item, it will have no effect upon future liquidity and cash flows. For the calculation of regulatory capital, core deposit intangible asset is disallowed and is a reduction to equity capital. The Company expects that disallowing this intangible asset should not materially adversely affect the Company’s regulatory capital ratios.

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The core deposit intangible asset is subject to significant estimates by management related to the value and the life of the asset. These estimates could change over time. The Company will review the valuation of this asset periodically to ensure that no impairment has occurred. If any impairment is subsequently determined, the Company will record the impairment as an expense in its consolidated statement of operations.

Non performing loans

At the acquisition date, Gulfstream had total non-accrual loans of $3.7 million and no loans that were past due 90 days or more and still accruing. All loans that were on non-accrual status and all loan relationships that were greater than $500,000 and identified as impaired as of the acquisition date were considered by CenterState’s management to be credit impaired and will be accounted for pursuant to ASC Topic 310-30. Loans identified as such had an aggregate principal balance of $40.6 million and an estimated fair value, as of the acquisition date, equal to $30.1 million.

Other real estate owned

As part of the acquisition, the Company acquired OREO with a fair value less estimated selling expenses of $3.4 million that Gulfstream obtained through foreclosure and repossession. Fair value was based on current appraisals (appraisals less than one year old). OREO is further delineated below. Amounts are in thousands of dollars.

Operating results and cash flows

Management has from time to time become aware of acquisition opportunities and has performed various levels of review related to potential acquisitions in the past. The GS acquisition was attractive to the Company for a variety of reasons including the following:

Based on these and other factors, including the level of support related to the acquired loans, the Company believes that the GS acquisition will have an immediate positive impact on its earnings.

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The total assets acquired, approximately $555 million, excluding goodwill, represented approximately 23% of the Company’s $2,416 million of total assets as of December 31, 2013, and total deposits assumed, approximately $479 million, represented approximately 23% of the Company’s $2,056 million of total deposits reported as of December 31, 2013. The Company believes that the transaction will improve net interest income, as the Company earns more from interest earned on its loans and investments than it pays in interest on deposits.

Liquidity and capital resources

The GS acquisition enhanced the liquidity position of the Company. The Company acquired $102 million of cash and cash equivalents. This addition to the Company’s balance sheet represents additional support for the Company’s liquidity needs.

Deposits with an estimated fair value of $479 million were also assumed. Of this amount approximately 37% is in noninterest bearing deposits, 37% is in money market accounts and the remainder is in checking accounts and regular savings accounts.

In the GS acquisition, the Company also assumed two Trust Preferred Securities totaling $10.0 million issued by GS that qualify for Tier 1 capital. Interest payments are due quarterly at a rate of LIBOR plus 1.90% on the $7 million trust preferred security and a rate of LIBOR plus 1.70% on the $3 million trust preferred security. The Company estimated the fair value of these instruments to approximate $6.7 million at the January 17, 2014 acquisition date.

At December 31, 2013, the Company and the Bank were considered “well-capitalized” based on calculations of relevant regulatory ratios. The Company and the Bank had the following capital ratios at December 3, 2013.

The acquisition of GS did not have a material adverse effect on the Company’s regulatory capital ratios. The Company and Bank remain “well-capitalized” after taking into consideration the results of the GS transaction

Financial Statements

Attached hereto as Exhibit 99.1 and incorporated by reference into this Item 9.01(a) are Gulfstream Bancshares, Inc. audited consolidated financial statements as of December 31, 2013 and 2012 and the years then ended.

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The pro forma consolidated condensed balance sheet presented below assumes the transaction occurred at December 31, 2013. Adjusting entries are explained below. Amounts are in thousands of dollars.

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Adjusting entries:

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The pro forma consolidated condensed income statement for the year ending December 31, 2013 presented below assumes the transaction occurred at the beginning of the period presented. Adjusting entries are explained below. Amounts are in thousands of dollars.

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Income Statements – reclassifications

The following reclassifications adjusted Gulfstream’s historical income statements to conform to CenterState’s historical income statements.

Income Statements – Pro Forma Adjustments

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Gulfstream owns two of its four banking locations and leases the other two. Based on recent appraisals, the two owned office buildings are carried on Gulfstream’s books at approximately current fair value. The lease terms of the other two locations approximate current fair value based on management’s estimates. As such, management did not record a fair value adjustment to these assets at the closing date of the merger and no adjustments have been made to the proforma combined condensed financial statements presented in this document.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

Date: March 12, 2014

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