Compound Interest Calculator
Growth of savings with monthly deposits. Change the numbers and the result updates instantly.
How it works
Compound interest means you earn interest on your earlier interest. Money grows faster the longer it stays invested. The formula for a lump sum is A = P(1 + r/n)^(nt); with monthly deposits the calculator adds the future value of each deposit.
Example
Example: $5,000 plus $300 a month at 7% for 20 years grows to about $176,472, of which only $77,000 is money you put in. Returns are not guaranteed.
Tips
- Change one input at a time to see what moves the result most.
- Use realistic rates. Check current averages before you decide.
- Results are estimates and do not replace advice from a licensed professional.
Frequently asked questions
Is this calculator free?
Yes. There is no sign-up and nothing is stored on our servers; the math runs in your browser.
How accurate is it?
It uses standard formulas, but real offers include fees, rate changes and taxes that can differ. Treat the result as an estimate.
Sources and method
Page last updated November 2026. See our editorial policy and disclaimer.