Compound Interest Calculator
See how compound interest grows your money over time. Enter a starting amount, an optional monthly contribution, your annual interest rate and the number of years to get the future value, the total interest earned, and a year-by-year breakdown.
How to use it
Enter your starting amount, any monthly contribution, the annual interest rate and the time horizon. The calculator compounds monthly and shows your projected balance, how much of it is your own money versus interest, and a chart of the balance climbing over time.
Compounding rewards time more than anything else — interest earns interest, so the curve steepens in later years. Try lengthening the horizon or adding a small monthly contribution to see how dramatically the final balance changes.
Frequently asked questions
How is compound interest calculated?
Each period, interest is added to the balance, and the next period's interest is calculated on that larger balance. This calculator compounds monthly: balance × (1 + rate/12) each month, plus any contribution.
Does it include monthly contributions?
Yes. Enter a monthly contribution and it's added at the end of each month, then compounds alongside your starting amount. Set it to zero to model a single lump sum.
What rate of return should I use?
Use a realistic long-run figure for your account type — savings and CDs are low single digits, while broad stock-market averages have historically been higher but vary year to year. Returns aren't guaranteed; this is an estimate.
BriskToolbox provides estimates for general information only and is not financial advice. Investment returns are not guaranteed.