Compound Interest Calculator
See how your savings grow with compound interest.
About Compound Interest Calculator
See how savings and investments grow over time when interest compounds. Compounding means you earn returns not just on your original principal but also on the interest already added, which is why long time horizons can produce dramatic growth. Enter a starting amount, an interest rate, a contribution schedule, and a number of years to project the future balance and see how much of it comes from interest versus your own deposits. It is a helpful way to compare scenarios, understand the impact of starting early, or set a savings goal. The figures are estimates for planning and all math runs locally in your browser.
How to use this tool
- 1Enter your starting amount (principal).
- 2Set the annual interest rate and how often it compounds.
- 3Optionally add a monthly contribution.
- 4Choose the number of years and see the final balance and total interest earned.
The rule of 72 and compounding frequency
A quick mental shortcut: divide 72 by your annual return to estimate how many years it takes money to double. At 6%, money doubles roughly every 12 years; at 9%, every 8 years.
| Annual rate | Compounded yearly | Compounded monthly |
|---|---|---|
| 4% | $21,911 | $22,226 |
| 6% | $32,071 | $33,102 |
| 8% | $46,610 | $49,268 |
| 10% | $67,275 | $73,281 |
Two takeaways: the rate matters enormously over long horizons (10% produces more than 3× the result of 4%), while compounding frequency matters much less than people assume - monthly vs. yearly compounding at 6% differs by only about 3% after 20 years.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and previously earned interest, which makes balances grow faster over time than simple interest.
Are monthly contributions included in the math?
Yes. Contributions are added each month and start compounding from that point forward.
Related guide
5 min readHow Compound Interest Works (With Simple Examples)
Understand compound interest, the formula behind it, and why starting early matters so much - with worked examples you can try yourself.