Compound interest calculator

See how a starting amount and monthly contributions grow over time. Free, private, runs in your browser.

How it works

The rate is converted to an equivalent monthly rate: i = (1 + r/n)n/12 − 1, where n is the compounding frequency. Each month: Balance = Balance × (1 + i) + Contribution (added at month end).

Without contributions this is the classic FV = P × (1 + r/n)n·t. Example: $1,000 at 5% compounded yearly for 10 years → $1,628.89. $100 a month at 6% compounded monthly for 10 years → $16,387.93.

Real returns vary year to year and are not guaranteed. Taxes, fees and inflation are not included.

Learn more

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FAQ

What is compound interest?

Interest earned on both your original money and on interest already earned, so growth speeds up over time.

When are contributions added?

At the end of each month. Contributions at the start of the month would grow slightly more.

What return should I use?

Use a conservative estimate. Past market returns do not guarantee future results, so try a few scenarios.

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