Company: SFNC
Filing Date: 2025-07-23
Form Type: 424B5
Source: 0001193125-25-162761
Chunk: 35

Company: SIMMONS FIRST NATIONAL CORP
Filing Date: 2025-07-23
Form: 424B5
Chunk 35
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                |     | $         |  0.9250 |     | $                 |  15,003,500 |     | $             |  17,254,025 |
| Proceeds to (before expenses) |     | $         | 17.5750 |     | $                 | 285,066,500 |     | $             | 327,826,475 |

| (1) | Represents underwriting discounts and commissions equal to five percent (5%) per share, which is the       
 underwriting discount we have agreed to pay on shares sold in this offering to investors introduced by the |

S-29

| underwriters. For shares sold in this offering pursuant to the directed share program, 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 differ from the amounts shown in the table above.                                                                     |

We estimate that our total offering expenses, excluding the underwriting discount, will be approximately $1,000,000. We have also agreed to reimburse the underwriters for certain of their reasonable out-of-pocketexpenses incurred in connection with their engagement as underwriters, including, without limitation, certain legal fees and expenses and marketing, syndication and travel expenses. We will not otherwise reimburse the underwriters for their legal fees in connection with this offering, except as may be required pursuant to any indemnification obligations. Directed Share Program 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. Lock-UpAgreements We, and each of our executive officers and directors, have agreed, for the period beginning on and including the date of this prospectus supplement through and including the date that is 90 days after the date of this prospectus supplement, without the prior written consent of Stephens Inc. and with Stephens Inc. providing prior written notice to the other representatives (email being sufficient), not to:

| • |     | offer, pledge, sell, contract to sell, sell any option or contract to purchase, purchase any option or contract                                                                                                                                           
 to sell, grant any option, right or warrant for the sale of, hypothecate, establish an open “put equivalent position” within the meaning of                                                                                                               
 Exchange Act Rule 16a-1(h), or otherwise dispose of or transfer