Compound Interest & Savings Calculator
Small monthly deposits grow faster than you think thanks to compounding. Enter what you can save and see the balance year by year.
Year-by-year breakdown
How it's calculated
Interest is compounded at the frequency you choose and converted to an equivalent monthly rate, g = (1 + r/k)k/12 − 1. Each month the balance earns g and then your deposit is added (deposits at month-end). Savings account rates (APY) change over time and investment returns are not guaranteed — the rate you enter is an assumption, not a forecast.
Questions & answers
What is the difference between APR and APY?
APY (annual percentage yield) already includes compounding; APR does not. Banks advertise savings accounts by APY. The "Effective annual yield" line above shows the APY that matches your rate and compounding.
How often does compounding matter?
Less than people think. At 5%, daily vs monthly compounding changes the effective yield by only a few hundredths of a percent. Deposit size, rate and time matter far more.
What is the rule of 72?
Divide 72 by the annual rate to estimate how many years it takes money to double. At 6%, about 12 years. It is a quick mental check on this calculator's results.
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