Money

401(k) Calculator

What a 401(k) contribution actually costs your paycheck after tax, and whether you are leaving employer match on the table.

Enter your salary and what percentage you contribute.

Annual salary

Your contribution

As a percentage of salary.

Filing status

How often you are paid

Your employer’s match

Match rate

50 means 50 cents per dollar.

Matched up to

Of your salary.

Project it forward

Current balance

Age

Years until retirement

Annual return

Estimate. A real-world figure based on the assumptions listed below, which you can change.

How this calculator works

Traditional 401(k) contributions come out before federal income tax, so contributing $100 does not reduce your take-home pay by $100. At a 22% marginal rate it costs you $78. People routinely decide they cannot afford to contribute based on the gross figure, which overstates the cost by exactly their tax rate.

The marginal rate here is worked out from your salary and filing status using the same published bracket data as the paycheck calculator, and it is applied to taxable income — after the standard deduction — rather than to gross salary. Using the gross rate is a common shortcut that overstates the saving for anyone near a bracket edge.

One thing is deliberately not counted as a saving: Social Security and Medicare are still withheld on 401(k) contributions. Only income tax is deferred. Calculators that add 7.65% to the saving are overstating it.

The second question is the employer match, and it matters more than the tax. A match is the highest guaranteed return available to you — a 50% match is an instant 50% on the money before a cent of investment growth. Contributing below your match cap forfeits it permanently; there is no catching it up next year.

The formula

Exactly what happens to your numbers, step by step.

What it costs you
```
take-home reduction = contribution × (1 − marginal rate)
```
Marginal rate on taxable income. FICA still applies, so it is not part of the saving.

The employer match

match = min(your %, match cap %) × salary × match rate

The limit
```
contribution = min(your % × salary, elective deferral limit)
```
Employer match sits on top and does not count against the limit.

A worked example

An $80,000 salary, single, paid every two weeks, with a 50% match up to 6%.

What you enter

Salary: $80,000
Contribution: 6%
Employer match: 50% up to 6%
Marginal rate: 22%

The working

You contribute: $4,800 a year
Tax deferred: $4,800 × 22% = $1,056
Take-home actually falls by: $3,744 — about $144 a paycheck
Employer adds: $2,400
Total into the account: $7,200

$7,200 into the account for $3,744 out of pocket — 1.92×

Before any investment return, before any compounding, the account gains nearly double what leaves your paycheck. Compare it with contributing 3% instead: that saves $72 a paycheck today, forfeits $1,200 of match every year, and over thirty years at 7% lands at $571,930 instead of $940,282. That $72 a fortnight is worth $368,352.

Assumptions

Every result here rests on these. Change your inputs and the result changes with them.

Contributions are traditional pre-tax, not Roth.
The marginal rate is derived from salary and filing status, using this year’s published brackets and the standard deduction.
Salary and contribution percentage stay level. No raises, no bonus deferrals.
The employer match is a straight percentage up to a cap, and you are fully vested.
The projection assumes a constant return with contributions made each pay period.

What this cannot tell you

State income tax is not included in the saving. Most states also allow the deferral, so your real saving is usually a little larger than shown.
Catch-up contributions are flagged if you are eligible but not modelled, because plans differ on whether they offer them and the rules changed recently for higher earners.
Vesting schedules are ignored. Employer match often vests over several years, and leaving early can mean forfeiting some of it.
It does not model Roth 401(k) contributions, which are taxed now and tax-free later — a different trade-off that depends on rates you cannot know.
It does not tell you whether you are on track to retire. That is a different question with different inputs, and the Retirement Calculator answers it.

Questions people ask

How much does contributing to a 401(k) actually reduce my paycheck?

By the contribution less your marginal tax rate. At 22%, contributing $400 a paycheck reduces take-home by $312. Enter your figures above for the exact amount — the per-paycheck number is usually the one that changes people’s minds.

How much should I contribute to get the full match?

At least up to your match cap, whatever the rest of your finances look like. A 50% match is an immediate 50% return, guaranteed, before any investment risk. Nothing else available to you pays that, and unclaimed match is gone for good.

Does the employer match count against the contribution limit?

No. The elective deferral limit applies to what you put in. Employer contributions sit on top of it, under a separate and much higher overall cap.

Do I save on Social Security and Medicare tax too?

No, and this is a common mistake. FICA is withheld on 401(k) contributions — only federal income tax is deferred. A calculator showing a saving of your marginal rate plus 7.65% is overstating it.

What happens if I contribute more than the limit?

Payroll normally stops your contributions once you hit it. If you changed jobs mid-year and exceeded it across two plans, you have to notify a plan administrator to return the excess before April 15 or it gets taxed twice. This calculator caps the figures at the limit and says so.

Sources and review

Sources

Methodology version 1.0.0 · Last reviewed September 10, 2026