Compound Interest Calculator

See how your money grows with compound interest and regular contributions, year by year.

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$
Contributions Made At
Fractions and decimals both work.
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Future Value
Total contributions
Interest earned
Effective annual rate (APY)
Doubling time
Interest Share

Growth by Year

Updates as you change the inputs.

YearContributionsInterestBalanceRemove

How Compound Interest Works

Compound interest earns interest on past interest. The more often it compounds, and the longer you leave it, the faster it grows.

Future value of the starting amount = P × (1 + r ÷ m)m × t
Future value of contributions = C × ((1 + i)n − 1) ÷ i

P is the starting amount, r the annual rate, m the compounding periods per year and t the years. For contributions, i is the interest rate per contribution period and n the number of contributions. Contributions at the start of each period earn one extra period of interest. Continuous compounding uses er × t.

Worked Example

Tips

This matches Excel's FV function when compounding and contributions are both monthly. Returns on stocks aren't a fixed rate, so treat long-term projections as estimates. Taxes and fees reduce real growth; inflation reduces what the money will buy.