Interactive tool · all calculations in your browser
Build a projection from assumptions you can inspect.
Enter a starting balance, an equal monthly deposit, a number of years, a constant annual effective return, and annual inflation. The browser calculates the illustration locally. The form does not send those values to the website.
Illustration only. It is not a forecast, guarantee, tax calculation, account limit checker, or individualized recommendation.
Interactive model
Set your scenario
Use your own assumptions. Nothing you enter here is sent to the site.
Projected future value
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| Year | Deposited | Balance |
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01 / FIELD NOTE
What the calculator assumes
The opening balance earns a constant effective annual return converted to an equivalent monthly rate. A contribution is added at the end of every month. The same deposit and return assumption continue for the entire period. No withdrawals, contribution pauses, contribution increases, employer match, changing fees, or changing returns are modeled.
02 / FIELD NOTE
The formula and timing
Let P be the opening balance, C the month-end contribution, n the number of months, and r the monthly effective return. The projected value is P × (1+r)^n + C × ((1+r)^n − 1) / r. When r is zero, the value is P + C × n. The calculator derives r as (1 + R)^(1/12) − 1 from the annual effective return R. Month-end contributions do not earn a return for the month in which they are added.
03 / FIELD NOTE
Inflation adjustment
For annual inflation assumption i over y years, the displayed present-value equivalent is the nominal future value divided by (1+i)^y. This is a simplified purchasing-power comparison. Actual inflation changes over time, and the mix of prices faced by a household may differ from a broad price index. The calculator does not forecast inflation or estimate future living costs.
04 / FIELD NOTE
How to read the outputs
Total contributions equal the starting balance plus the scheduled deposits. Modeled growth is the difference between the future value and those contributions under the selected assumptions. The annual table and chart show interpolated checkpoints from the monthly calculation. A negative return is permitted; a zero return uses the separate arithmetic case.
05 / FIELD NOTE
What is excluded
The tool excludes taxes, investment and plan fees, account eligibility, annual contribution limits, employer matching, vesting, required distributions, benefit payments, Social Security, withdrawals, and changes in deposits or returns. The result can differ substantially from an actual account, including because an investment may lose value.
06 / FIELD NOTE
Choosing assumptions responsibly
A return input is a scenario, not a claim about what a portfolio will earn. Consider comparing multiple assumptions rather than selecting one as “expected.” Do not use this model alone to decide how much to contribute, which investment to buy, whether to claim a benefit, or when to retire. Check plan terms, IRS rules, and professional advice for personal decisions.