401(k) Contribution Calculator

The one decision that matters more than the rest

Almost every piece of retirement advice is a judgment call — how much risk to take, which fund to pick, whether to lean traditional or Roth. Capturing your full employer match is not one of those judgment calls. If your plan matches 50% of your contributions up to a certain percentage of salary, and you contribute less than that percentage, your employer's other hand is literally holding money out to you that you are choosing not to take. That match lands in your account before any investment return even begins — it is closer to a guaranteed, instant return than almost anything else available to an ordinary saver. Increasing a contribution rate until it clears the match threshold is one of the few moves in personal finance with essentially no downside case.

This calculator's "money left on the table" figure exists for exactly that reason. A general-purpose compound interest calculator can project growth on a contribution, but it has no idea your employer will add money on top of it if you contribute a little more. This tool does, because it models the match tiers directly.

How the annual contribution limit works

The IRS caps how much you personally can defer from your own paycheck into a 401(k) each year — $24,500 for 2026. That limit applies only to your elective deferral, the amount withheld from your salary. It does not apply to your employer's match, which is calculated and added on top without touching your personal limit at all. There is a separate, much higher ceiling on the combined total of your contributions and your employer's — the IRC Section 415(c) limit — but it is set high enough that it rarely matters to anyone below a very high income, and this calculator does not attempt to model it.

If the contribution percentage you enter, applied to your salary, would produce a dollar amount above the limit for your age that year, this calculator caps the modelled contribution at the legal limit instead of quietly showing a number you could not actually contribute. Watch for the notice above the results panel — it only appears when capping actually happened somewhere in your projection.

Catch-up contributions after 50

Turning 50 unlocks an extra amount you can defer on top of the standard limit — $8,000 for 2026. A newer SECURE 2.0 provision, in effect since 2025, replaces that with a larger enhanced catch-up specifically for the years you are 60, 61, 62 or 63: $11,250 for 2026. At 64 the allowance reverts to the standard 50-and-over catch-up. Both figures are modelled in this calculator, confirmed directly against the IRS's 2026 cost-of-living adjustment notice, and the projection applies each one only from the calendar year you actually reach the qualifying age — never retroactively, and never for years before you get there.

Traditional vs. Roth, briefly

This calculator assumes a traditional, pre-tax 401(k): your contribution lowers your taxable income today, and the entire balance — contributions and growth alike — is taxed as ordinary income when you withdraw it in retirement. A Roth 401(k) flips that: you contribute after-tax dollars now, and qualified withdrawals in retirement, growth included, come out completely tax-free. The projection maths here — contribute, match, grow — is identical either way. Only what happens at withdrawal differs, and this tool does not attempt to model which one leaves you better off, since that depends on a comparison between your tax rate now and your expected tax rate in retirement.

For the immediate effect a traditional 401(k) has on this year's paycheck — it lowers federal and state income tax withholding but not Social Security or Medicare — see the paycheck calculator. This tool picks up where that one stops, projecting the balance forward instead of showing this period's withholding.

The return assumption is a planning input, not a promise

Same caveat as every growth projection on this site: the annual return you enter is an assumption, not a guarantee. A long-run diversified stock allocation has historically averaged somewhere around 7% after inflation, but that average is built from decades that include sharp individual down years. A 401(k) projection spanning 20 or 30 years has more time to absorb that volatility than a short-term goal does, but it is still an estimate. Run the numbers again at a more conservative rate before treating any single figure here as a plan.

What this calculator does not include

• Vesting schedules — employer contributions in many plans belong to you only after a set number of years of service, which this projection does not model.
• Plan fees and fund expense ratios, which quietly reduce the return you actually receive relative to the headline rate you enter.
• The separate, much higher combined employer-and-employee limit under IRC Section 415(c), which ordinary earners rarely reach.
• The tax differences between traditional and Roth contributions — see the section above.
• Job changes, rollovers, loans against the balance, or early withdrawals, all of which can interrupt a real projection in ways this steady, uninterrupted model does not capture.