Employees who look at their W-2 often notice that Box 1 (federal taxable wages) and Box 3 (Social Security wages) don't match, and the common assumption is that one of the two must be wrong. Usually both are correct. The two boxes follow different rules: 401(k) contributions reduce Box 1 but not Box 3, while Section 125 pre-tax benefit elections reduce both. Box 3 has an annual cap (the Social Security wage base, $184,500 in 2026) while Box 1 has no cap. Understanding the differences matters because Box 3 drives the Social Security tax the employee actually paid and the earnings that will count toward their future Social Security benefit.
What Social Security Wages Actually Include Box 3 includes regular wages, most bonuses, commissions, taxable fringe benefits, and tips (which also appear separately in Box 7). It also includes imputed income from taxable items like group-term life insurance over $50,000 and personal use of a company vehicle. It does not include pre-tax cafeteria plan contributions under Section 125 (health, dental, vision premiums, FSA contributions, dependent care FSA).
Unlike Box 1, Box 3 is not reduced by 401(k) or other qualified retirement plan elective deferrals. An employee who contributes $20,000 to their 401(k) sees Box 1 lower than their total wages by $20,000 but sees Box 3 at the full amount.
How the Annual Wage Base Caps Box 3 Box 3 is capped at the Social Security wage base each year. For 2026, the cap is $184,500, up from $176,100 in 2025. Once an employee's year-to-date Social Security wages cross the cap, no additional wages get added to Box 3, and the employer stops withholding Social Security tax for the rest of the calendar year.
Medicare wages (Box 5) are typically higher than Box 3 for high earners because Medicare tax has no cap. Box 5 often matches Box 3 for employees earning less than the wage base.
Why Do Box 1 and Box 3 Sometimes Show Different Amounts? Primarily because 401(k) elective deferrals reduce Box 1 but not Box 3. The reverse also happens: certain fringe benefits (like adoption assistance up to the annual exclusion) reduce Box 1 but not Box 3. Employees sometimes see Box 3 higher than Box 1 because of this.
Common Box 3 Errors Including pre-tax Section 125 elections that should have reduced Box 3. Excluding taxable benefits that should have been added. Continuing to add wages to Box 3 after the employee crossed the wage base. Treating elective deferrals (401(k)) as Social Security-exempt (they aren't).
Each of these errors produces either an under- or over-statement of Social Security tax owed, which leads to either an employee refund request or an IRS correction letter. Errors typically get caught during tax season, when employees file their 1040 and see the discrepancy.
Getting Box 3 Right at Year-End Reconcile Box 3 totals against the sum of Form 941 Social Security wages for all four quarters. Any discrepancy greater than rounding signals a reporting error that needs correction before W-2 distribution. Review employees near the wage base carefully; the most common error is continuing withholding past the cap.
Pair Box 3 verification with broader payroll reconciliation, W-2 form preparation, and FICA compliance workflows. Reference the IRS W-2 and W-3 instructions , the SSA contribution and benefit base page , and the IRS Publication 15 for the authoritative rules on what belongs in Box 3 and what doesn't.
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