Compound Interest Calculator

What it does

Grows a balance at a fixed annual rate, compounding as often as you choose — annually, monthly, daily — and adds your regular deposits along the way. It splits the result into what you put in versus the interest earned, and shows the effective annual yield (APY): the rate you actually earn once compounding is counted, which is always a touch higher than the stated (nominal) rate.

Who this helps

Anyone with a fixed-rate vehicle: a high-yield savings account, CD, money-market fund, or bond. It's the right tool when the rate is known and steady — for variable market returns, use the Investment Return Calculator instead.

How to use it

1. Enter your starting principal and any regular deposit.
2. Set the annual rate and how often it compounds — banks quote APY, which already bakes in the frequency.
3. Pick a horizon and read the future value, total interest, and the nominal-vs-APY comparison.

What it doesn't do

Assumes the rate never changes — real savings and CD rates move. It doesn't model taxes on interest (interest is usually taxed as ordinary income each year), nor inflation. Use the Inflation Eroder to see the result in today's purchasing power.