UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, DC 20549

FORM 8-K/A

(Amendment No. 1)

CURRENT REPORT PURSUANT TO

SECTION 13 OR 15(d) OF THE

SECURITIES EXCHANGE ACT OF 1934

Date of earliest event reported: August 31, 2015

SMARTFINANCIAL, INC.

(Exact Name of Registrant as Specified in its Charter)

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):

¨   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))

EXPLANATORY NOTE

This Amendment No. 1 on Form 8-K/A (this “Amendment”) amends Item 9.01 of the Current Report on Form 8-K filed by SmartFinancial, Inc., a Tennessee corporation formerly known as Cornerstone Bancshares, Inc. (the “Company”) on September 2, 2015 (the “Original Report”), in which the Company reported, among other events, the completion of its merger (the “Merger”) with SmartFinancial, Inc., a Tennessee banking corporation (“Legacy SmartFinancial”). This Amendment provides (i) the historical financial statements required by Item 9.01(a) and (ii) the unaudited pro forma financial information required by Item 9.01(b) that were omitted from the Original Report in reliance on Item 9.01(a)(4) and Item 9.01(b)(2), respectively. This Amendment does not amend any other item of the Original Report or purport to provide an update or a discussion of any developments at the Company subsequent to the filing date of the Original Report. All information contained in the Original Report is subject to updating and supplementing as provided in the Company’s reports filed with the Securities and Exchange Commission subsequent to the date on which the Original Report was filed.

The audited financial statements of Legacy SmartFinancial as of and for the years ended December 31, 2014 and 2013, including the reports of its independent accounting firm, Maudlin & Jenkins, LLC, and the unaudited financial statements of Legacy SmartFinancial as of June 30, 2015 and for the six months ended June 30, 2015 and 2014 are filed herewith as Exhibit 99.1 and incorporated herein by reference.

The Merger is treated as a reverse acquisition for accounting purposes. Therefore, Legacy SmartFinancial is deemed to have acquired the Company for accounting purposes, and the historical financial statements of Legacy SmartFinancial have become the Company’s historical financial statements pursuant to generally accepted accounting principles.

The pro forma effect of the Merger on the Company is described in the unaudited pro forma combined condensed balance sheet of the Company at June 30, 2015, the unaudited pro forma combined condensed statements of income of the Company for the six months ended June 30, 2015 and for the year ended December 31, 2014, and the notes thereto that are filed herewith as Exhibit 99.2 and incorporated herein by reference.

The exhibits filed with this report are listed in the Exhibit Index that immediately follows the signature hereto, which Exhibit Index is incorporated herein by reference.

SIGNATURES

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.

EXHIBIT INDEX