Compound Interest Calculator

Compound interest is interest calculated on both the original amount and the interest already added to it. Each period, the interest is added to the balance, so the next period's interest is a little larger. Over long periods this snowball effect does most of the work.

This calculator lets you choose how often interest compounds, from yearly to daily, and add a fixed amount every month. It shows the final value, how much you put in, the interest earned, the effective yearly rate and a year-by-year chart and table. It works for savings, deposits, bonds or any fixed-rate growth.

With no deposits, the amount after t years is A = P × (1 + r ÷ n)^(n × t), where r is the yearly rate and n the number of times a year interest is added. More frequent compounding gives a slightly higher effective yearly rate: 8% compounded monthly works out to 8.30% a year.

Monthly deposits are added at the end of each month and grow at the same rate, converted to its monthly equivalent so every compounding frequency is treated consistently.