401(k) Paycheck Impact Calculator 2026
See what raising your 401(k) contribution costs your take-home pay, and why the cost is always less than the amount you save.
How this is calculated
Your employer does not settle your tax bill once a year. It withholds from every paycheck using the percentage method the IRS publishes in Publication 15-T, and this calculator runs the same steps in the same order.
Gross pay for the period is worked out first. Pre-tax deductions come off next, and this is where most free calculators go wrong: a traditional 401(k) contribution reduces the wages your income tax is figured on, but it does not reduce the wages Social Security and Medicare are figured on. A health premium, HSA or FSA contribution reduces both, because those sit inside a Section 125 cafeteria plan.
What remains is annualised, reduced by the standard deduction for your filing status, and run through the federal bracket table. Dependent credits are subtracted, then the result is divided back down to your pay period and any extra W-4 withholding is added. State tax is calculated separately on its own base with its own deduction and brackets. Post-tax items such as Roth 401(k) and garnishments come off last, and what is left is your net pay.
A dollar saved costs less than a dollar
A traditional 401(k) contribution comes out before federal and, in most states, state income tax. At a 22% federal and 5% state marginal rate, $200 into the plan reduces take-home pay by about $146. The other $54 is tax you did not pay.
What it does not escape is FICA. Social Security and Medicare are calculated on gross pay less Section 125 items only, and a 401(k) is not one of those, so the full 7.65% still applies. That is the single most common error in free paycheck calculators, and it is why a 401(k) contribution and an HSA contribution of the same size produce different net pay.
Traditional against Roth, on the paycheck
A Roth 401(k) contribution is taken after tax. The same $200 reduces take-home pay by the full $200, and no tax is due on the withdrawal in retirement. A traditional contribution costs less now and is taxed later.
On the paycheck the choice is simple arithmetic: traditional if your marginal rate now is higher than you expect it to be in retirement, Roth if it is lower. Enter both figures in the deductions section above to see the difference on your own numbers, or read the full comparison.
The match, and the limit
Contribute at least enough to collect the full employer match. A 50% match on the first 6% of pay is an immediate 50% return that no other line on your paycheck offers. Anything below the match threshold is money left behind.
Pennsylvania is the exception worth knowing: it does not exempt 401(k) deferrals from state income tax, so a Pennsylvania resident sees the federal saving but not a state one. This calculator handles that correctly.
2026 tax rates used on this page
| Item | Rate | Limit or threshold |
|---|---|---|
| Social Security (OASDI) | 6.2% | First $184,500 of wages, maximum $11,439 |
| Medicare | 1.45% | No cap |
| Additional Medicare | 0.9% | Wages above $200,000 single, $250,000 joint, $125,000 separate |
| Federal income tax | 10% to 37% | Seven brackets, after the standard deduction |
| Standard deduction | — | $16,100 single, $32,200 joint, $24,150 head of household |
| Federal supplemental rate | 22% | Applied to bonuses under the flat method |
| Dependent credits | — | $2,000 per child under 17, $500 per other dependent |
Sources: IRS Rev. Proc. 2025-32 and the Social Security Administration 2026 announcement. Verified 17 September 2026.
2026 federal brackets
| Rate | Single | Married filing jointly |
|---|---|---|
| 10% | $0 to $12,400 | $0 to $24,800 |
| 12% | $12,400 to $50,400 | $24,800 to $100,800 |
| 22% | $50,400 to $105,700 | $100,800 to $211,400 |
| 24% | $105,700 to $201,775 | $211,400 to $403,550 |
| 32% | $201,775 to $256,225 | $403,550 to $512,450 |
| 35% | $256,225 to $640,600 | $512,450 to $768,700 |
| 37% | $640,600 and above | $768,700 and above |
Frequently asked questions
How does a 401(k) affect my paycheck?
A traditional 401(k) contribution reduces the wages your federal and most state income tax is calculated on, so your take-home pay falls by less than the amount you contribute. At a combined 27% marginal rate, $200 contributed costs about $146 of net pay.
Does a 401(k) reduce Social Security and Medicare tax?
No. FICA is calculated on gross pay less Section 125 items such as health premiums, HSA and FSA. A 401(k) contribution is not one of those, so the full 6.2% Social Security and 1.45% Medicare still apply.
How much should I contribute?
At minimum, enough to collect the full employer match, which is the highest guaranteed return available on a paycheck. Beyond that the answer depends on your marginal rate now against your expected rate in retirement, and on competing goals such as debt and an emergency fund.
What is the difference between a traditional and a Roth 401(k) on my paycheck?
Traditional contributions come out pre-tax, so take-home pay falls by less than the contribution. Roth contributions come out after tax, so take-home pay falls by the full amount. Both are subject to FICA, and both usually receive the same employer match.
Does my state give the same 401(k) break as the federal government?
Most do, because they start from federal taxable wages. Pennsylvania does not exempt elective deferrals, so Pennsylvania residents pay the 3.07% state tax on contributions. New Jersey treats some deferrals differently as well.
What happens if I hit the annual contribution limit?
Payroll stops the deduction for the rest of the year, which raises your take-home pay for those periods and can reduce a percentage-based employer match if the match is calculated per period. Spreading contributions evenly across the year avoids that.
Related calculators
These figures are estimates for informational purposes and are not tax advice. Actual withholding depends on your employer’s payroll system, your year-to-date wages and your specific W-4. Federal rates come from IRS Rev. Proc. 2025-32 and the SSA 2026 announcement; state rates come from each state’s own withholding guide, with the source and verification date published on every state page. Read the methodology, or see who maintains this data.