Compound Interest Calculator
Enter a starting amount, rate, and time to see how it grows, live as you type.
What this tool does
This tool projects how an initial amount grows over time when it earns compound interest — interest calculated not just on the original principal but on the interest already earned. Add an optional monthly contribution to model regular saving or investing, pick how often interest compounds, and the future value, total interest earned, and total amount contributed all update live as you type.
Example use case
$10,000 invested at a 7% annual return, compounded monthly, with an extra $200 contributed every month, grows to a noticeably larger balance over 10 years than the same $10,000 left untouched — this tool shows exactly how much of that final balance came from your own contributions versus interest earned on top of them.
How compounding frequency affects growth
The more often interest compounds — daily versus annually, for example — the faster a balance grows at the same nominal annual rate, since each compounding period's interest starts earning interest of its own sooner. The difference is usually small for typical savings rates and timeframes, but it grows with higher rates and longer horizons.