Company: SFNC
Filing Date: 2025-07-23
Form Type: 424B5
Source: 0001193125-25-162761
Chunk: 1

Company: SIMMONS FIRST NATIONAL CORP
Filing Date: 2025-07-23
Form: 424B5
Chunk 1
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 we have agreed to pay underwriting discounts and      
 commissions equal to three percent (3%) per share. As a result, the actual total underwriting discount and net proceeds to us may be lower and higher, respectively, than the amounts shown above. The underwriters will also be reimbursed for certain 
 expenses incurred in this offering. See “Underwriting” for details.                                                                                                                                                                                     |

At our request, the underwriters have reserved up to 811,000 shares of our common stock offered by this prospectus supplement for sale at the public offering price through a directed share program to certain of our executive officers and directors. See “Underwriting — Directed Share Program.” We have granted the underwriters an option, exercisable not later than 30 days after the date of this prospectus supplement, to purchase up to an additional 2,433,000 shares of common stock from us on the same terms and conditions set forth above. None of the SEC, any state securities commission or banking agency, the Federal Deposit Insurance Corporation (the “FDIC”), the Board of Governors of the Federal Reserve System (the “Federal Reserve”) or any other regulatory body has approved or disapproved of these securities or passed upon the accuracy or adequacy of this prospectus supplement or the accompanying prospectus. Any representation to the contrary is a criminal offense. Shares of our common stock are not savings accounts, deposits or other obligations of any of our bank or non-banksubsidiaries, and are not insured or guaranteed by the FDIC or any other governmental agency. The underwriters are offering the shares of our common stock as set forth in the “Underwriting” section of the prospectus supplement. The underwriters expect to deliver the shares of common stock in book-entry form only through the facilities of The Depository Trust Company, against payment on or about July 23, 2025. Joint Book-Running Managers

| Stephens Inc. |     | Keefe, Bruyette & Woods 
 A Stifel Company        |     | Morgan Stanley |

Co-Managers

| Baird |     | Raymond James |

The date of this prospectus supplement is July 21, 2025.

TABLE OF CONTENTS Prospectus Supplement

|                                                                 |     | Page |      |
| About This Prospectus Supplement and the Accompanying           
 Prospectus                                                      |     |      | S-ii |
| Where You Can Find More Information                             |     |      | S-1  |
| Incorporation by Reference                                      |     |      | S