Compound interest calculator
See how savings grow with regular deposits.
About this calculator
Compound interest means you earn interest on past interest as well as on what you deposit. The chart separates what you pay in from what the balance earns, which shows how much of the growth comes from time.
The return you enter stays the same every year. Real investment returns go up and down, and tax and inflation are not included.
How it works
Each month the balance earns interest at a rate equivalent to your chosen compounding, then your deposit is added.
Worked example
- Starting amount: $10,000
- Monthly deposit: $300
- Annual return: 6%
- Time: 20 years
- Compounding: Monthly
Balance after 20 years: $171,714
The story behind it
Where the idea came from: Jacob Bernoulli, Swiss mathematician, 1683.
In 1683, Jacob Bernoulli asked a simple money question: what happens if interest is added more and more often? The answer levels off at a limit, and that limit is the number now called e, about 2.718. His question is still the heart of saving: interest that earns interest. This calculator shows how much of your final balance comes from that effect.
Why you can trust this calculator
- It runs in your browser. Nothing you type into it is sent anywhere.
- The method is explained on this page, so you can check it yourself.
- Free to use, with no sign-up.
- Results are estimates, not financial advice.
- Spotted a mistake? Tell us and we'll look into it.
After 15 years as a mathematics educator, I built CalculStore to give students, teachers, professionals and anyone working with numbers simple, reliable tools.
Meet the founder