Compound Interest Calculator
See how your money grows over time with compound interest and regular contributions. Adjust the rate and horizon to watch the snowball effect.
Updated June 2026 · Reviewed by the apitpi team · How we calculate
Balance after 20 years
$225,974
$143,974 of that is compound growth
- Total contributed
- $82,000
- Interest earned
- $143,974
Why time matters most
The longer your money compounds, the more of your final balance comes from growth rather than contributions. Starting even a few years earlier can mean tens of thousands more at the finish line — which is why the time horizon often matters more than the exact return rate.
Frequently asked questions
What is compound interest? +
Compound interest is interest earned on both your original money and the interest it has already earned. Over time this snowball effect can grow your savings dramatically faster than simple interest.
How is compound growth calculated here? +
We compound monthly: each month your balance earns interest at your annual rate divided by 12, then your monthly contribution is added. The chart shows total balance versus the money you actually contributed.
What return rate should I use? +
It depends on your investments. Historically, a diversified stock market portfolio has returned roughly 7–10% per year before inflation, while savings accounts return far less. Use a rate that matches where your money is invested.