401(k) Retirement Calculator
Free to use, with no sign up. Your entries stay in this browser; calculations run on your device.
Result
A = P(1 + r/n)^(nt) + Σ C(1 + r/n)^[n(t − tₖ)]. P = entered balance, r = entered annual return / 100, n = compounding periods/year, C = each monthly contribution, tₖ = its deposit time in years.
OpenStax Contemporary Mathematics: compound interest explains the principal formula. Contributions sum the same growth formula from each deposit time. This model assumes a constant entered rate and contributions at the end of each month.
Worked example: An entered balance of $25,000, $500 monthly contributions, a fixed 6.5% annual return and 30 years gives $727,883.99: $205,000 entered and $522,883.99 modeled interest.
This is arithmetic on entered numbers. It does not include taxes, employer match rules, contribution limits or withdrawal rules. The fixed return is an assumption, not a forecast. Amounts are USD; results round to cents without rounding intermediate interest. Contributions are made at each month end. The table includes full years and any final fractional year.
Arithmetic only; not financial advice.
Related calculators: Compound Interest Calculator, Investment Calculator, Retirement Income Calculator.
How to use this tool
Enter the balance you want to model, a monthly contribution, a fixed annual return and the number of years. Select Calculate to see the projected balance, total entered contributions and year-by-year balances.
Frequently asked questions
Does this predict my 401(k) balance?
No. It applies the fixed return and monthly contribution you enter as arithmetic; actual results can differ.
Does this include taxes or plan rules?
No. It does not include taxes, employer match rules, contribution limits or withdrawal rules.
Is this calculator free and private?
Yes. Arithmetic runs in your browser without uploading your entries or saving them to browser storage.