Compound Interest Calculator

Each period, interest is added to the balance, so the next period earns interest on it too: A = P(1 + r/n)^(nt) for a lump sum, plus the future value of each deposit. $10,000 plus $500 a month at 7% compounded monthly grows to about $462,000 in 25 years, of which $160,000 is your own money.

Less than most people expect. At 7%, monthly compounding gives an APY of 7.229% and daily compounding 7.25%. On the example above that is about $1,500 extra after 25 years — the rate, the time and how much you add matter far more than the compounding schedule.

Use the Reach a goal tab. With $10,000 to start, a 7% return and 25 years, you need about $1,164 a month. Starting 10 years earlier or adding a yearly raise lowers the monthly amount sharply, and the tool recalculates instantly as you change the inputs.

It divides the future balance by the growth of prices over the same years, so you can judge its real buying power. At 2.5% inflation, $462,000 in 25 years buys about what $249,000 buys today. Set your own inflation rate under Inflation & currency.

A shortcut for doubling time: divide 72 by the annual rate. At 7% that is about 10.3 years; the exact figure using the effective yield is 9.9 years. The calculator shows both so you can see how close the shortcut is at your rate.

Yes. It is free with no sign-up, and every calculation runs in your browser, so nothing is sent or stored. Results assume a steady rate; real investment returns vary, and taxes and fees are not included, so treat them as estimates rather than financial advice.