Is the 401k calculator free?
Yes. It is completely free to use, with no signup, no account, and no paywall.
How accurate are the results?
The calculator uses the standard formulas for this kind of math, but real-world results can differ once fees, rounding, rate changes, and provider-specific rules come into play. Treat the output as a planning estimate, not a quote.
Does it stay local?
Yes. The numbers you enter are processed entirely in your browser and never leave your device.
Why does this give a different answer from the retirement calculator here?
Different compounding. This tool compounds once a year and adds the whole contribution at year end. The retirement calculator compounds monthly on a monthly contribution, so each deposit starts growing sooner. Given equivalent inputs, the monthly model always returns the higher balance, and the annual model is the more conservative of the two.
Does it enforce the IRS contribution limit?
No. The field accepts any number. Employee deferral limits are set annually by the IRS and rise with a catch-up allowance from age 50, and separate limits govern total employer plus employee contributions. Check your plan documents before modelling a figure you cannot actually contribute.
Is the projected balance before or after tax?
Before, for a traditional 401(k). Contributions go in pre-tax and withdrawals are taxed as ordinary income, so the headline balance overstates your spending power. A Roth 401(k) is the reverse, funded with after-tax money and withdrawn tax free, and the tool does not distinguish between the two.
Where does my employer match go?
Into the annual contribution field, added to your own deferral. If you defer 8000 and your employer matches 50% up to 4000, enter 12000. There is no separate field and no vesting logic, so unvested employer money is counted as though it were already yours.
What return rate should I use?
The tool takes no view, and the 7% default is a common long-run nominal assumption for a diversified equity-heavy portfolio before fees and before inflation. Subtract your fund's expense ratio, and subtract your inflation assumption again if you want the result in today's money.