Are 401(k) Contributions Subject to FICA Taxes?

On payday, imagine a worker who just increased their 401(k) contribution and opens their pay stub expecting every tax line to shrink. Federal income-tax withholding looks lower, but Social Security and Medicare taxes barely move. This is a common, composite scenario many employees encounter, not an account of any specific person. If money goes straight into retirement savings before income taxes, why is FICA still being withheld?

The short answer is yes. Employee 401(k) contributions are generally subject to FICA taxes, which include Social Security and Medicare taxes. A traditional, pre-tax 401(k) contribution can reduce current federal income-tax withholding, but it does not reduce the wages used to calculate FICA taxes.

How 401(k) Contributions Are Treated for FICA

FICA stands for the Federal Insurance Contributions Act, the law covering payroll taxes for Social Security and Medicare. When an employee defers part of their pay into a 401(k), that money generally remains part of wages for FICA purposes, even though it may be excluded from current income-tax calculations.

The IRS draws a clear line between income-tax treatment and FICA treatment:

• Traditional pre-tax employee deferrals: subject to FICA, generally not subject to current federal income-tax withholding.
• Roth employee deferrals: subject to FICA and subject to current federal income-tax withholding.
• Employer matching and nonelective contributions: generally not subject to FICA or federal income-tax withholding when contributed.

The IRS states these rules directly in its retirement-plan contribution FAQ.

A Simple Paycheck Example

Consider an employee earning $2,000 in a biweekly paycheck who contributes $200 to a traditional 401(k). For federal income-tax withholding, payroll generally calculates the tax on $1,800, the wages remaining after the deferral. But for Social Security and Medicare purposes, payroll generally still uses the full $2,000, because the deferral does not reduce FICA wages.

This is why an employee might see federal income-tax withholding calculated on a lower amount while Social Security and Medicare taxes look almost the same as before the 401(k) increase. The IRS's 401(k) participant resource guide confirms that elective deferrals are excluded from current income for federal income-tax purposes, yet remain wages subject to Social Security, Medicare, and federal unemployment taxes. A consumer-friendly summary from NerdWallet reaches the same conclusion: employees still pay Medicare and Social Security taxes on money they contribute to a 401(k).

Traditional vs. Roth 401(k): What Changes?

Both traditional and Roth 401(k) employee contributions are subject to FICA. The difference lies in federal income-tax treatment.

Contribution type	Subject to FICA?	Subject to current federal income-tax withholding?
Traditional 401(k) employee deferral	Yes	Generally no
Roth 401(k) employee deferral	Yes	Yes
Employer match or nonelective contribution	Generally no	Generally no

Choosing between traditional and Roth contributions is not a choice about avoiding Social Security or Medicare tax. Both are included in FICA wages. The decision mainly concerns when federal income tax applies to the employee's own contributions.

Employer Contributions Are Different

Employer matching and nonelective contributions are treated differently from what an employee defers. According to the IRS contribution FAQ, these employer contributions are not subject to FICA or federal income-tax withholding at the time they are made, since the employee did not elect to defer that money from their own paycheck.

Two simple questions can clarify the treatment:

• Did the employee contribute part of their own pay? If so, the deferral is generally subject to FICA.
• Did the employer add money to the plan? If so, that contribution is generally not subject to FICA when made.

What Employees Should Check on a Pay Stub

Reviewing a pay stub can make this treatment easier to understand. Look for separate fields such as gross wages, traditional 401(k) contribution, Roth 401(k) contribution, Social Security wages or tax, Medicare wages or tax, federal income-tax withholding, and employer retirement contribution or match.

A traditional deferral may reduce wages used for federal income-tax withholding while Social Security and Medicare wages stay closer to gross pay. A Roth deferral usually does not reduce current federal income-tax wages, since it is made with after-tax dollars. Pay stub formats vary by employer and payroll provider, so labels may differ. If a line item is unclear, ask payroll or benefits staff how the fields are calculated.

A Special Consideration for Catch-Up Contributions

FICA wages also matter for certain 401(k) catch-up contribution rules. Fidelity explains that if an employee is age 50 or older and has FICA-taxable earnings of $150,000 or more, catch-up contributions must be made to a Roth 401(k) with after-tax dollars under the rules it describes. Fidelity also notes that FICA earnings differ from modified adjusted gross income (MAGI). See Fidelity's overview of Roth 401(k) catch-up rules.

Employees approaching catch-up eligibility should review plan communications and ask their benefits team how the plan applies these earnings thresholds.

Payroll Takeaways for Employers

For employers, accurate treatment starts with recognizing that employee 401(k) deferrals remain FICA wages. Payroll processes should distinguish among traditional deferrals, Roth deferrals, and employer contributions so withholding and wage reporting align correctly. A short explanation that “pre-tax” refers to current federal income-tax treatment, not FICA exemption, can prevent confusion when employees compare their 401(k) election with their pay stub. Employers managing payroll across multiple locations should also confirm that U.S. FICA rules are applied separately from other jurisdictions' requirements.

The Bottom Line

Employee 401(k) contributions, both traditional and Roth, are generally subject to FICA taxes. Traditional contributions can lower current federal income-tax withholding, but not Social Security or Medicare taxes. Employer matching and nonelective contributions are generally not subject to FICA when made. When in doubt, employees should review their pay stub and plan materials, while employers should confirm payroll systems classify each contribution type correctly.

Informational note: This article is provided for general informational purposes only and is not legal advice. It does not represent the advice or opinion of the website or organization on which it appears.