Compound Interest Calculator
Simulate investments and savings with compound interest. Find out how much your money can grow over time.
The compound interest calculator shows how an invested amount grows over time when each period's interest starts earning interest too, not just the original amount. Enter the initial amount, an optional monthly contribution, the interest rate and the term to see the final amount, how much you invested in total, and how much came from interest.
How to use
- Enter the initial amount you already have to invest (can be zero).
- If you plan to invest every month, enter the monthly contribution amount.
- Fill in the interest rate and term, choosing whether they're monthly or yearly, and watch the result update automatically.
Frequently asked questions
What's the difference between simple and compound interest?
With simple interest, returns are always calculated on the original amount. With compound interest, each period's return becomes part of the amount that earns interest in the next period too, leading to faster growth over time.
How is a yearly rate converted to monthly?
We use compound conversion: the equivalent monthly rate is calculated so that, applied 12 times in a row, it produces the same yearly rate you entered — not just the yearly rate divided by 12.
At what point in the month is the contribution applied?
We assume the contribution is made at the end of each month, a common model used in investment simulators.