Compound interest

Future value of a starting balance plus monthly contributions.

Quick answer: This calculator projects a future value from a starting balance plus a monthly contribution at an annual return you type, compounded monthly. The sample is $10,000, $400 a month, 8% a year, for 30 years. 8% is an example, not a forecast.

Starting balance Monthly contribution Annual return % Years

Monthly compounding: each month the balance grows by annual return ÷ 12, then the contribution is added. This is not a tax-adjusted return. Educational only.

What this means for you

What this means for you: the headline is the balance if the return repeats every month. Contributions are what you put in. Growth is the gap. The return is not reduced for fees or taxes.

How to use this calculator

Open the Compound interest calculator and keep the sample numbers or replace them with your own. The result updates as you type.
Read the headline figure first, then the breakdown or chart under it.
Use Copy share link if you want those inputs in the URL. The page is an educational estimate, not a filing, approval, or recommendation.

FAQ

How does this compound interest calculator work?

Each month it grows the balance by the annual return divided by 12, then adds the contribution.

Is 8% a promised return?

No. It is the sample so the page is not blank. Type the rate you want to test.

Does this subtract taxes or fund fees?

No. It is a pre-tax, pre-fee projection. A taxable account or a fund expense ratio would land lower.

Educational, not financial advice. Page updated October 24, 2026 — no tax, limit, or rate figure was changed in this review.