Are 401(k) Contributions Subject to FICA? Employee vs. Employer

Yes, 401(k) contributions are subject to FICA when they come out of your paycheck. Every dollar you defer into a 401(k), whether traditional pre-tax or Roth, gets the 6.2% Social Security tax and 1.45% Medicare tax taken out before it reaches your retirement account. Employer matching contributions are the exception: they skip FICA entirely.¹

Your Own Deferrals Always Get Hit With FICA

The rule is statutory. IRC Section 3121(v)(1)(A) explicitly folds employer contributions made under a qualified cash or deferred arrangement (the legal name for a 401(k)) back into the definition of “wages” for FICA purposes. In plain English, the tax code overrides any exclusion that might otherwise shelter your deferral from payroll taxes.²

This applies across the board. Traditional deferrals get FICA taken out. Roth deferrals get FICA taken out. Catch-up contributions for workers 50 and older get FICA taken out. So do the enhanced “super catch-up” amounts SECURE 2.0 opens up for workers aged 60 through 63.³ If it comes off your paycheck as an elective deferral, Social Security and Medicare take their share first.

What It Looks Like on a Paycheck

Say you earn $2,000 in a biweekly pay period and defer $200 into a traditional 401(k). Your employer runs FICA on the full $2,000: $124 for Social Security (6.2%) and $29 for Medicare (1.45%). The $200 deferral only shrinks the amount used to figure your federal income tax withholding, so income tax is calculated on $1,800. The FICA line items on your pay stub reflect gross pay, not the reduced figure.

Employer Contributions Skip FICA

Employer matching contributions and non-elective contributions to your 401(k) are not subject to FICA when deposited into the plan.¹ The IRS treats your deferrals as wages you chose to redirect, but treats the employer’s match as a benefit that was never part of your compensation for payroll tax purposes.

Employer contributions also escape federal income tax withholding when deposited. The tax comes later. When you withdraw employer money and its investment earnings in retirement, you pay ordinary income tax on the full amount. FICA is never charged on those funds, at contribution or at withdrawal.

Why “Pre-Tax” Does Not Mean “No FICA”

The confusion comes from the tax code using two separate definitions of “wages” depending on which tax is being figured. Both FICA and income tax withholding sit under Subtitle C of the Internal Revenue Code, but they rely on different rules.⁴

FICA wages under Section 3121 include your elective deferrals. Section 3121(v)(1)(A) adds 401(k) contributions back into the wage base so they get taxed for Social Security and Medicare.²
Income tax withholding wages under Section 3401 exclude payments to a qualified trust, which is why your traditional 401(k) deferral reduces the wages your income tax withholding is calculated on.⁵

When people call traditional 401(k) contributions “pre-tax,” they mean pre-income-tax. The contribution really does lower your taxable income for federal income tax purposes, and that is a valuable benefit. But the label misleads people into thinking no taxes touch the money at all. FICA still takes its share from the full gross amount.

Roth 401(k) contributions work the same way for FICA. Since Roth contributions are already after-tax dollars for income tax purposes, they appear in both the income tax and FICA calculations. There is no scenario where an employee’s elective deferral escapes FICA.

Checking Your W-2

Your year-end W-2 makes the split easy to see. If you contributed to a traditional 401(k), Box 1 (Wages, tips, other compensation) will be lower than Box 3 (Social Security wages) and Box 5 (Medicare wages). The gap is roughly the amount of your traditional deferrals.⁶

The W-2 instructions confirm this directly: elective deferrals to a 401(k) plan are excluded from Box 1 but must be reported in Boxes 3 and 5.⁶ Your total deferral also shows up in Box 12 under Code D. If Boxes 1, 3, and 5 all match and you made traditional 401(k) contributions, something may be off with your employer’s payroll reporting.

Roth 401(k) contributions do not create the same gap because they are included in Box 1 along with Boxes 3 and 5. All three boxes reflect the same underlying wage figure.

The Social Security and Medicare amounts should be calculated on your full gross wages, not the reduced figure after 401(k) contributions. An error here can affect both your tax filings and your Social Security earnings record.

The Upside of Paying FICA on Your Deferrals

Paying FICA on your 401(k) deferrals is not pure downside. Because those contributions count as FICA wages, they get included in the earnings your employer reports to the Social Security Administration each year.⁷ Your future Social Security benefit is calculated from your highest 35 years of indexed earnings. If 401(k) deferrals were exempt from FICA, that money would drop out of your earnings record and could shrink your monthly benefit in retirement.

This matters most for workers deferring large amounts. Someone contributing $24,500 in a year sees that full amount reflected in their Social Security earnings history. The 1983 Social Security Amendments specifically kept 401(k) deferrals inside the payroll tax base to prevent that kind of benefit erosion.⁸

Self-Employed Workers and Solo 401(k)s

If you are self-employed and contribute to a solo 401(k), the same principle reaches you through a different tax. Instead of FICA, you pay self-employment tax under IRC Section 1401, which combines the employee and employer shares into a single 15.3% rate (12.4% for Social Security plus 2.9% for Medicare).

Your elective deferral to a solo 401(k) does not reduce your self-employment tax. The deferral is calculated after SE tax has already been applied to your net earnings. You get the income tax deduction for the contribution, just as a W-2 employee would, but your Social Security and Medicare obligations do not budge.⁹ The retirement deferral escapes income tax now but never escapes the payroll tax equivalent.

1
Internal Revenue Service. Retirement Plan FAQs Regarding Contributions
2
Office of the Law Revision Counsel. 26 U.S. Code 3121 – Definitions
3
Internal Revenue Service. 401(k) Limit Increases to $24,500 for 2026
4
Office of the Law Revision Counsel. 26 U.S. Code Subtitle C Chapter 24 – Collection of Income Tax at Source on Wages
5
Office of the Law Revision Counsel. 26 U.S. Code 3401 – Definitions
6
IRS. General Instructions for Forms W-2 and W-3 (2026)
7
Social Security Administration. Contribution and Benefit Base
8
Social Security Administration. What Determines 401(k) Participation and Contributions?
9
Internal Revenue Service. Publication 560 (2025), Retirement Plans for Small Business