Published July 28, 2026

How 401(k) Contributions Affect Your Take-Home Pay

One of the most common paycheck questions is: "If I increase my 401(k) contribution, how much smaller will my take-home pay actually get?" The answer is usually smaller than people expect, because of how pre-tax contributions interact with your taxable income.

Pre-tax contributions reduce your taxable income first

A traditional 401(k) contribution comes out of your paycheck before federal (and often state) income tax is calculated. That means a $100 contribution doesn't reduce your take-home pay by the full $100 — it reduces it by $100 minus the tax you would have paid on that $100. If you're in a 22% federal bracket, a $100 contribution might only cost you around $75-80 in actual take-home pay, with the rest effectively coming from taxes you would have paid anyway.

Roth 401(k) contributions work differently

Roth 401(k) contributions come out after tax, so a $100 Roth contribution does reduce your take-home pay by the full $100 today — but withdrawals in retirement are typically tax-free, versus traditional 401(k) withdrawals which are taxed as income later. Which one is "better" depends on whether you expect to be in a higher or lower tax bracket in retirement than you are now.

Don't leave employer match on the table

If your employer matches contributions (a common structure is matching 50% or 100% of your contribution up to a percentage of your salary), not contributing enough to get the full match is effectively leaving free money unclaimed. This is usually the first thing worth checking before optimizing anything else about your paycheck.

FICA taxes still apply

One nuance: 401(k) contributions reduce your federal (and often state) taxable income, but they do not reduce the income subject to Social Security and Medicare (FICA) taxes. Those are calculated on your gross wages regardless of retirement contributions.

Model it before you change your contribution rate

Because the real impact on your take-home pay is smaller than the sticker amount you're contributing, it's easy to either over- or under-estimate the effect. Before adjusting your contribution percentage, run your salary and expected contribution through our take-home pay calculator to see the actual per-paycheck difference — so you can set a contribution rate you can comfortably live with month to month.