W-2 Box 4 — Social security tax withheld

Tax return implications

• Generally isn't deducted or credited on your 1040 by itself — it's already-paid FICA tax, not income tax withholding.
• If combined Box 4 across multiple employers exceeds the annual maximum, the excess is a dollar-for-dollar credit on Form 1040, Schedule 3, Line 11 — it directly reduces your tax or adds to your refund.
• A single employer's over-withholding does not qualify for the Schedule 3 credit; that requires correction from the employer (Form W-2c) or a refund claim on Form 843.
• If you also have self-employment income, your W-2 Box 3 wages count toward the wage base before Schedule SE computes the 12.4% Social Security portion of your self-employment tax.
• Employees in a FICA-replacement public retirement system can legitimately show $0 in Box 4, matching a $0 in Box 3.

Common pitfalls & things to check

• Don't look for the 0.9% Additional Medicare Tax here — it never touches Box 4. That surcharge is Medicare-only and shows up in Box 6 and on Form 8959.
• Don't claim a Schedule 3 excess-Social-Security credit for a single employer's overwithholding — that credit is only available when the excess comes from combining wages across two or more employers.
• A common missed refund: people who changed jobs mid-year and forget to check whether their combined Box 4 crossed the annual maximum — that credit doesn't get claimed automatically.
• $0 in both Box 3 and Box 4 usually means a FICA-exempt government retirement plan, not a missing W-2 entry — confirm with payroll rather than assuming an error.
• If Box 4 isn't within a few cents of 6.2% of (Box 3 + Box 7), treat it as a payroll error and request a W-2c before you file — an incorrect Box 4 can throw off your Schedule 3 computation.

Related W-2 boxes