Are 401(k) Contributions Subject to FICA Taxes?

Yes. Employee contributions to a 401(k), whether traditional or Roth, are generally subject to Social Security and Medicare taxes, which together make up FICA. A traditional contribution can reduce the amount of pay subject to current federal income-tax withholding, but it does not reduce the wages used to calculate FICA. A Roth contribution is also subject to FICA and is generally included in current federal income-tax wages. Employer matching and nonelective contributions are generally not subject to FICA when contributed. The distinction matters when you compare your contribution election with your pay stub or estimate how much a 401(k) contribution will change take-home pay.

How 401(k) Contributions Are Treated for FICA

FICA is the Federal Insurance Contributions Act tax for Social Security and Medicare. When an employee directs part of their pay into a 401(k), that employee deferral generally remains part of FICA wages even if a traditional deferral is excluded from current federal income-tax wages.

The tax treatment depends on the contribution type. Traditional employee deferrals are generally subject to FICA but excluded from current federal income-tax withholding calculations. Roth employee deferrals are subject to both FICA and current federal income-tax withholding. Employer matching and nonelective contributions are generally excluded from both FICA and federal income-tax withholding when contributed.

The IRS explains this distinction in its retirement-plan contribution FAQ. It is also important not to confuse FICA with federal income tax. These are separate payroll taxes with different rules, as explained in this guide to FICA and federal income tax.

How the Difference Appears in a Paycheck

Suppose an employee earns $2,000 in a biweekly paycheck and contributes $200 to a traditional 401(k). For current federal income-tax withholding, payroll generally excludes the $200 deferral and calculates withholding using $1,800. For Social Security and Medicare purposes, payroll generally still counts the full $2,000 as wages.

As a result, increasing a traditional contribution may reduce federal income-tax withholding without producing a similar reduction in Social Security or Medicare taxes. The IRS 401(k) participant resource guide confirms that elective deferrals are excluded from current federal income-tax wages but remain subject to Social Security and Medicare taxes. It also notes that these deferrals remain subject to federal unemployment tax. NerdWallet provides a consumer-friendly explanation of the same distinction.

Traditional and Roth 401(k) Contributions

Both traditional and Roth employee contributions are generally subject to FICA. The difference is when federal income tax applies to the employee's contribution. Traditional contributions are generally made before current federal income tax is calculated. Roth contributions are made with after-tax dollars and are generally included in current federal income-tax wages.

Choosing between traditional and Roth contributions is therefore not a way to avoid Social Security or Medicare taxes. The choice primarily changes the timing of federal income tax on the employee's contributions. For a related comparison involving another type of payroll contribution, see whether HSA contributions are subject to FICA.

How Employer Contributions Are Treated

Employer matching and nonelective contributions are treated differently from amounts an employee defers from their own pay. They are generally not subject to FICA or federal income-tax withholding at the time they are contributed. The IRS FAQ distinguishes these employer contributions from employee elective deferrals.

A useful way to understand the distinction is to ask whose money is being contributed. If the employee elected to defer part of their wages, the deferral is generally subject to FICA. If the employer adds a match or nonelective contribution, that amount is generally not subject to FICA when contributed.

What to Check on a Pay Stub

Pay stubs may show gross wages, retirement contributions, Social Security wages, Medicare wages, tax withholding, and employer contributions in separate fields. The labels and layout vary by payroll provider. A guide to what a pay stub shows can help explain the different sections.

For a traditional deferral, federal income-tax wages may be lower than gross pay while Social Security and Medicare wages remain closer to gross pay. A Roth deferral generally does not reduce current federal income-tax wages. If a pay-stub line is unclear, ask payroll or benefits staff how that field is calculated.

How FICA Wages Affect Catch-Up Contributions

FICA wages can also matter for certain 401(k) catch-up contribution rules. Fidelity explains that beginning in 2026, employees age 50 or older whose FICA wages from the employer in the prior year exceed the applicable threshold must make catch-up contributions as Roth contributions. The threshold described is $150,000 and is subject to annual adjustment. FICA wages for this purpose are not the same as modified adjusted gross income. See Fidelity's overview of Roth 401(k) catch-up rules for details.

This rule concerns the tax treatment of catch-up contributions, not whether regular employee 401(k) contributions are subject to FICA. Employees approaching catch-up eligibility can review plan communications to see how the plan handles the applicable earnings threshold.

What Employers Should Consider in Payroll

Payroll processes should distinguish employee traditional deferrals from Roth deferrals and employer contributions. Employee deferrals generally remain FICA wages even when traditional deferrals reduce current federal income-tax wages. Correct classification helps align withholding and wage reporting with the contribution type.

Explaining that “pre-tax” refers to current federal income-tax treatment can also help employees understand why Social Security and Medicare taxes may not decrease when they raise a traditional 401(k) contribution. Employers operating across jurisdictions should apply U.S. FICA treatment separately from the rules that apply elsewhere.

*This article is for general informational purposes only and is not legal advice.