WINTRUST FINANCIAL CORP — Earnings Release 2013

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

Current Report

Pursuant to Section 13 or 15(d) of The

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): July 16, 2013

WINTRUST FINANCIAL CORPORATION

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (847) 939-9000

Not Applicable

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

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:

¨ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

¨ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

¨ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

¨ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Item 2.02. Results of Operations and Financial Condition

The information in this Current Report is being furnished and shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section. The information in this Current Report shall not be incorporated by reference into any registration statement or other document pursuant to the Securities Act of 1933, as amended.

On July 16, 2013, Wintrust Financial Corporation (the “Company”) announced earnings for the second quarter of 2013 . A copy of the press release relating to the Company’s earnings results is attached hereto as Exhibit 99.1. Certain supplemental information relating to non-GAAP financial measures reported in the attached press release is included on pages 13 and 14 of Exhibit 99.1.

Item 9.01. Financial Statements and Exhibits

(d) Exhibits

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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: July 16, 2013

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INDEX TO EXHIBITS

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