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Compound Interest Calculator
See how your savings or investments grow over time with compound interest and regular monthly contributions.
How compound interest works
With compound interest you earn interest on your interest. Each period, the interest earned is added to your balance, so the next period's interest is calculated on a bigger number. Over long periods this snowball effect does most of the work.
The formula for a single deposit is A = P × (1 + r/n)n×t, where P is the starting amount, r the yearly rate, n the number of times interest compounds per year and t the number of years. $10,000 at 7% compounded monthly for 20 years grows to about $40,400.
The rule of 72
Divide 72 by your interest rate to estimate how many years it takes to double your money. At 6%, money doubles in about 12 years; at 9%, about 8 years.
Frequently asked questions
How much will $500 a month be worth in 30 years?
At a 7% yearly return compounded monthly, saving $500 a month for 30 years grows to about $610,000, of which $180,000 is your own money.
What is the difference between APR and APY?
APR is the simple yearly rate. APY includes the effect of compounding, so it is a little higher. 5% APR compounded monthly equals about 5.12% APY.