How a 401(k) Contribution Affects Your Paycheck (2026)

This article is for general information, not tax or financial advice. Contribution limits and tax brackets change most years. Verify current figures with the IRS or your plan administrator, and talk to a tax professional before making decisions.

You are sitting in open enrollment, staring at a box that wants a percentage. You know you should save for retirement. What you actually want to know is simpler: if you put in 5%, how much smaller will your next paycheck be?

A traditional 401(k) costs your paycheck less than you might expect. The contribution comes out before income tax is calculated, so part of it is offset by a lower tax bill. But there is a catch most articles skip, and it explains why the drop is still bigger than the simple tax math predicts. Let’s walk through the whole thing.

Your paycheck drops by less than you contribute

With a traditional 401(k), a dollar you defer is excluded from your taxable wages. It is not taxed for federal income tax now, and usually not for state income tax either.

So the money you put in does not come straight out of your take-home dollar for dollar. Some of it is money you would have paid in tax anyway.

Here is the rule of thumb. In the 22% federal bracket, $1.00 of traditional 401(k) costs you roughly $0.78 of take-home pay. In the 12% bracket it costs closer to $0.88. The higher your marginal rate, the cheaper each contributed dollar feels in the moment.

A quick example: defer $200 a paycheck in the 22% bracket and your take-home drops by about $150, not the full $200. The other $50 is income tax you no longer owe right now.

Traditional vs. Roth 401(k): why one shrinks your tax bill and the other doesn’t

Your plan probably offers two flavors, and they hit your paycheck very differently.

A traditional 401(k) is pre-tax. The contribution is taken out before income tax is figured, so it lowers your taxable wages today. You pay income tax later, when you withdraw the money in retirement.

A Roth 401(k) is after-tax. The contribution comes out of pay that has already been taxed, so it gives you zero current tax relief, and your take-home drops by the full amount you contribute.

The trade is simple. Traditional saves you tax now and taxes you later. Roth costs you the full amount now and comes out tax-free in retirement.

For your immediate paycheck, the practical difference is this: a $300 traditional deferral might lower take-home by about $230, while a $300 Roth deferral lowers it by the full $300. Same retirement savings, different bite today.

The FICA catch: 401(k) money still gets hit by Social Security and Medicare

This is the part most guides gloss over, and it is the reason your paycheck math never quite matches the marginal-rate shortcut.

Your paycheck actually uses two different wage bases. One is for income tax, and a traditional 401(k) deferral does lower it. The other is for FICA (Social Security and Medicare), and a 401(k) deferral does not lower it at all.

FICA is 7.65% total: 6.2% for Social Security up to the annual wage base, plus 1.45% for Medicare with no cap. That 7.65% is calculated on your full gross wages, before your 401(k) comes out.

So when you defer $200 to a traditional 401(k), you still pay Social Security and Medicare tax on that $200. Only the income tax is reduced. That is exactly why a $200 deferral lowers take-home by around $150 rather than by some larger number you would get if you imagined the whole contribution dodging every tax.

So a traditional 401(k) trims income tax, not payroll tax. Roth contributions are also fully subject to FICA, since they are after-tax to begin with.

A line-by-line paycheck example

Numbers make this concrete. Take a biweekly employee with $2,500 in gross pay per check, single filer, in a state with a flat 5% income tax. Assume a 12% federal withholding rate on the taxable portion for simplicity. Here is the same paycheck with and without a $250 traditional 401(k) deferral (10% of gross).

| Line | No 401(k) | With $250 traditional 401(k) | |---|---|---| | Gross pay | $2,500.00 | $2,500.00 | | Pre-tax 401(k) | $0.00 | $250.00 | | Federal taxable wages | $2,500.00 | $2,250.00 | | Federal income tax (12%) | $300.00 | $270.00 | | State income tax (5%) | $125.00 | $112.50 | | FICA (7.65% of gross) | $191.25 | $191.25 | | Net take-home | $1,883.75 | $1,676.25 |

Look at the FICA line. It does not move. The 401(k) deferral knocked $30 off federal tax and $12.50 off state tax, for $42.50 in total tax savings.

Now compare the take-home. It fell by $207.50, even though you contributed $250. That $42.50 gap is your tax savings landing back in your pocket. The contribution “cost” you $207.50 of spendable pay to put $250 into retirement.

That is the entire mechanic in one table: gross, minus pre-tax deferral, gives a smaller income-tax base, while FICA quietly stays on the full gross.

2026 contribution limits and catch-up rules

Limits climbed for 2026, so the numbers in older articles are likely out of date.

• Base elective deferral limit: $24,500 for 2026, up from $23,500 in 2025.
• Standard catch-up (age 50+): $8,000, for a total of $32,500.
• Super catch-up (ages 60 to 63): $11,250 under SECURE 2.0, for a total of $35,750. This replaces the standard catch-up during those four ages, not in addition to it.

One more 2026 change matters for high earners. Starting January 1, 2026, if you earned more than $150,000 from your employer in the prior year, your catch-up contributions must go into a Roth account rather than pre-tax. Those catch-up dollars no longer reduce your current taxable income, so high earners near that line should expect a slightly larger paycheck hit on the catch-up portion.

These are annual limits across all your contributions to the plan, whether you elect a percentage or a flat dollar amount.

Don’t forget the employer match (and how to estimate your own number)

The employer match is the closest thing to free money in your paycheck. A common formula is 100% of the first 3% you contribute plus 50% of the next 2%, but every plan differs.

The match does not come out of your take-home. Your employer adds it on top of your pay and deposits it into your account. The only catch is that you usually have to contribute enough of your own money to unlock the full match, so contributing at least up to the match is the standard advice.

State taxes are worth a note too. In most states a traditional 401(k) deferral lowers your state taxable wages just like it lowers the federal base. A few states do not follow that rule. Pennsylvania, for example, taxes 401(k) contributions when you make them, so your state line would not drop there.

That state-by-state variation is exactly why a generic rule of thumb only gets you so far. To see your real number, you have to run your own gross, filing status, state, and contribution against the actual withholding tables.

That is what the WorkLogs44 Payroll Calculator is built to do. You enter a traditional or Roth 401(k) deduction as a flat dollar amount or a percentage, and it shows the live breakdown from gross to net for your state, with FICA calculated correctly on the full gross. You can model 4% versus 6% versus 10% in seconds and watch the take-home line respond.

If you want to try different contribution rates side by side before you commit, you can model them with the calculator tools, then download the app to keep your own numbers handy. For more on the payroll math behind your stub, browse our other guides.

Frequently Asked Questions

How much will my paycheck decrease if I contribute 5% to my 401(k)?

Less than 5% of your gross pay, if it is a traditional 401(k). The pre-tax deferral lowers your income-tax withholding, so part of the contribution is offset by a smaller tax bill. The exact drop depends on your marginal bracket and your state.

Does a 401(k) contribution lower my Social Security and Medicare taxes?

No. FICA of 7.65% is calculated on your full gross wages. Traditional 401(k) deferrals only reduce your income-tax wages, not your Social Security and Medicare wages, so the FICA line on your stub stays the same.

Does contributing to a 401(k) reduce my taxable income?

Yes for a traditional 401(k). Each dollar you defer is excluded from your federal taxable wages, and from your state taxable wages in most states. A Roth 401(k) does not reduce your taxable income, because it is contributed after tax.

What is the difference in paycheck impact between a traditional and a Roth 401(k)?

A traditional 401(k) shrinks your taxable income now, so your take-home falls by less than the contribution. A Roth 401(k) is after-tax, so your take-home falls by the full contribution amount with no current tax break.

How much can I contribute to my 401(k) in 2026?

The 2026 elective deferral limit is $24,500 if you are under 50. Add an $8,000 catch-up at age 50 or older, for $32,500. Ages 60 to 63 get a super catch-up of $11,250 instead, for a total of $35,750.

Will my employer’s 401(k) match reduce my paycheck?

No. The match is money your employer adds on top of your pay. It does not come out of your take-home. To earn the full match you usually have to contribute enough of your own pay to qualify for it.

Why is my take-home pay reduced by more than my tax savings suggest?

Because FICA is still withheld on your full gross wages. Only the income-tax portion of a traditional deferral is given back to your paycheck, so the take-home drop is larger than your income-tax savings alone would imply.

Ready to see your own number? Get WorkLogs44 and model your exact 401(k) take-home impact for your state and filing status.

Frequently Asked Questions

How much will my paycheck decrease if I contribute 5% to my 401(k)?

Less than 5% of your gross pay, if it is a traditional 401(k). The pre-tax deferral lowers your income-tax withholding, so part of the contribution is offset by a smaller tax bill. The exact drop depends on your marginal bracket and your state.

Does a 401(k) contribution lower my Social Security and Medicare taxes?

No. FICA of 7.65% is calculated on your full gross wages. Traditional 401(k) deferrals only reduce your income-tax wages, not your Social Security and Medicare wages, so the FICA line on your stub stays the same.

Does contributing to a 401(k) reduce my taxable income?

Yes for a traditional 401(k). Each dollar you defer is excluded from your federal taxable wages, and from your state taxable wages in most states. A Roth 401(k) does not reduce your taxable income, because it is contributed after tax.

What is the difference in paycheck impact between a traditional and a Roth 401(k)?

A traditional 401(k) shrinks your taxable income now, so your take-home falls by less than the contribution. A Roth 401(k) is after-tax, so your take-home falls by the full contribution amount with no current tax break.

How much can I contribute to my 401(k) in 2026?

The 2026 elective deferral limit is $24,500 if you are under 50. Add an $8,000 catch-up at age 50 or older, for $32,500. Ages 60 to 63 get a super catch-up of $11,250 instead, for a total of $35,750.

Will my employer's 401(k) match reduce my paycheck?

No. The match is money your employer adds on top of your pay. It does not come out of your take-home. To earn the full match you usually have to contribute enough of your own pay to qualify for it.

Why is my take-home pay reduced by more than my tax savings suggest?

Because FICA is still withheld on your full gross wages. Only the income-tax portion of a traditional deferral is given back to your paycheck, so the take-home drop is larger than your income-tax savings alone would imply.