Company: SFBC
Filing Date: 2025-05-02
Form Type: DEFA14A
Source: 0001541119-25-000020
Chunk: 0

Company: Sound Financial Bancorp, Inc.
Filing Date: 2025-05-02
Form: DEFA14A
Chunk 0
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<div align='center'>UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549</div>

#### SCHEDULE 14A INFORMATION
<div align='center'>Proxy Statement Pursuant to Section 14(a) of the Securities

Exchange Act of 1934 (Amendment No._)</div>

Filed by the Registrant ☒

Filed by a party other than the Registrant ☐

Check the appropriate box:

☐ Preliminary Proxy Statement

☐ Confidential, for Use of the Commission Only (as permitted by Rule 14a-6(e)(2))

☐ Definitive Proxy Statement

☒ Definitive Additional Materials

☐ Soliciting Material Pursuant to §240.14a-12

#### SOUND FINANCIAL BANCORP, INC.
<div align='center'>(Name of Registrant as Specified In Its Charter)

(Name of Person(s) Filing Proxy Statement, if other than the Registrant)</div>

Payment of Filing Fee (Check all boxes that apply):

| ☒ |     | No fee required                                                                                      |
| ☐ |     | Fee paid previously with preliminary materials                                                       |
| ☐ |     | Fee computed on table in exhibit required by Item 25(b) per Exchange Act Rules 14a-6(i)(1) and 0-11. |

### SOUND FINANCIAL BANCORP, INC.

#### 2400 3

#### rd

#### Avenue, Suite 150

#### Seattle, Washington 98121
<div align='center'>(206) 448-0884</div>

### SUPPLEMENT TO PROXY STATEMENT

### FOR ANNUAL MEETING OF SHAREHOLDERS

### TO BE HELD ON

#### MAY 27, 2025
On April 16, 2025, Sound Financial Bancorp, Inc. (the “Company”) filed with the Securities and Exchange Commission (the “SEC”) and made available to shareholders its definitive proxy statement (the “Proxy Statement”) relating to the Company’s 2025 Annual Meeting of Shareholders (the “Annual Meeting”), to be held on May 27, 2025, at 10:00 a.m. Pacific Time.

The Proxy Statement correctly identified the Annual Meeting date as May 27, 2025; however, due to a clerical error, the day of the week was incorrectly stated in two places (in the “Notice of Annual Meeting of Share