EXHIBIT 99.3

Consolidated Unaudited Pro Forma Financial Information

The following unaudited pro forma condensed combined financial information and explanatory notes show the impact on the historical financial positions and results of operations of Mercantile Bank Corporation (“Mercantile”) and Firstbank Corporation (“Firstbank”) and have been prepared to illustrate the effects of the merger of Firstbank with and into Mercantile. The merger, while considered a merger of equals, is accounted for as an acquisition by Mercantile of Firstbank using the acquisition method of accounting and, accordingly, the assets and liabilities of Firstbank were recorded at their respective fair values on June 1, 2014, the Merger Date. The merger was effected by the issuance of shares of Mercantile stock to Firstbank shareholders. Each share of Firstbank common stock was converted into the right to receive one share of Mercantile common stock, with cash in lieu of fractional shares. Immediately after consummation of the merger, Mercantile shareholders owned approximately 52% of the voting stock of the combined company.

The following unaudited pro forma combined consolidated statements of operations for the three months ended March 31, 2014 and the year ended December 31, 2013 combine the historical financial statements of Mercantile and Firstbank. The unaudited pro forma financial statements give effect to the merger as if the merger occurred on January 1, 2013 with respect to the statements of income for the three months ended March 31, 2014 and the year ended December 31, 2013. The unaudited pro forma financial statements were prepared with Mercantile treated as the “accounting acquirer” and Firstbank as the “accounting acquiree,” consistent with accounting for the merger as an acquisition under the acquisition method of accounting. The consideration transferred to complete the merger has been allocated to Firstbank’s assets and liabilities based upon their estimated fair values as of the date of completion of the merger. The fair values represent our best estimate based on available information and facts and circumstances in existence on the Merger Date. The fair values employed herein are subject to change for up to one year after the closing date of the transaction if information unknown relative to closing date fair values becomes available. The pro forma calculations shown below assume a closing price of $21.43, which represents the closing price of Mercantile’s common stock on May 30, 2014.

The pro forma income statement and per share data do not include anticipated cost savings or revenue enhancements, nor do they include one-time merger and integration expenses which will be expensed against income. It is expected that total merger-related costs will be approximately $12.1 million, primarily incurred during the second and third quarters of 2014. The pro forma combined basic earnings and diluted earnings per share of Mercantile common stock are based on the pro forma combined net income per common share for Mercantile and Firstbank divided by the pro forma common shares and diluted shares of the combined entities, respectively.

Certain reclassification adjustments have been made to Firstbank’s unaudited pro forma financial statements to conform to Mercantile’s financial statement presentation. The unaudited pro forma information, while helpful in illustrating the financial characteristics of the combined company under one set of assumptions, is presented for illustrative purposes only and is not necessarily indicative of the combined and consolidated financial position or combined and consolidated results of operations of Mercantile that would have been reported had the acquisition occurred on the dates indicated, nor do they represent a forecast of the combined and consolidated financial position of Mercantile at any future date or the combined and consolidated results of operations of Mercantile for any future period.

The unaudited pro forma condensed combined financial statements should be read together with: the accompanying notes to the unaudited pro forma condensed combined financial information; Mercantile’s separate audited historical consolidated financial statements and accompanying notes as of December 31, 2013 and 2012, and for the three years ended December 31, 2013, 2012 and 2011, included in Mercantile’s December 31, 2013 Form 10-K and the final prospectus dated November 6, 2013 filed pursuant to Rule 424(b) included herein; Firstbank’s separate audited historical consolidated financial statements and accompanying notes as of December 31, 2013 and 2012, and for the three years ended December 31, 2013, 2012 and 2011 included in Firstbank’s December 31, 2013 Form 10-K; Mercantile’s separate unaudited historical consolidated financial statements and accompanying notes as of and for the three months ended March 31, 2014 included in Mercantile’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2014; Mercantile’s separate unaudited historical consolidated financial statements and accompanying notes as of and for the three and six months ended June 30, 2014 included in Mercantile’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2014; and Firstbank’s separate unaudited historical consolidated financial statements and accompanying notes as of and for the three months ended March 31, 2014 included in Firstbank’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2014.

Mercantile has not presented a pro forma balance sheet as of March 31, 2014 as the transaction is reflected in the balance sheet for the quarter ended June 30, 2014.

Unaudited Combined Pro Forma Statement of Operations for the three months ended March 31, 2014

Unaudited Combined Pro Forma Statement of Operations for the twelve months ended December 31, 2013

Notes to Unaudited Pro Forma Combined Financial Statements

The following table provides the purchase price calculation as of the Merger Date and the identifiable assets purchased and the liabilities assumed at their estimated fair values. These fair value measurements are provisional based on third-party valuations that are currently under review and are subject to refinement for up to one year after the Merger Date based on additional information that may be obtained by us that existed as of the Merger Date.

Purchase Price:

Preliminary Statement of Net Assets Acquired at Fair Value: