Compound Interest Calculator
See how a starting balance and regular deposits grow over time. Enter your numbers and the future value, total deposits, and interest earned update as you type — with a year-by-year breakdown.
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Show year-by-year breakdown
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How to use the compound interest calculator
Type in your starting amount — the money you already have saved or invested. Add a regular deposit if you plan to keep paying in, and choose whether you add it monthly or yearly. Enter the annual interest rate you expect and the number of years you'll leave it to grow. The future balance updates instantly — there's no button to press and nothing is sent anywhere.
The big number is your projected balance at the end of the term. Below it you'll see how much came from your own deposits versus how much is interest earned on top — the part that compounding is doing for you.
Deposit timing (optional). Deposits added at the start of each period earn one extra period of interest, so the balance is slightly higher than adding them at the end. Most people use the end-of-period default.
Everything runs in your browser — the numbers you type are never uploaded. These figures are estimates based on a fixed rate, not financial advice; real returns vary.
Common compound interest questions
What is compound interest? Compound interest is interest earned on both your original money and on the interest it has already earned. Because each period's interest is added to the balance, the balance grows faster over time than with simple interest.
How is compound interest calculated? The future value of a starting amount is principal × (1 + r/n)^(n×t), where r is the annual rate, n is how many times interest compounds per year, and t is the number of years. Regular deposits are added each period and earn interest from then on. This calculator adds both together.
What is the difference between simple and compound interest? Simple interest is paid only on the original amount, so it grows in a straight line. Compound interest is paid on the original amount plus accumulated interest, so the balance grows faster and faster over time.
How much will $10,000 grow in 20 years? At 7% a year compounded monthly, $10,000 with no further deposits grows to roughly $40,000 in 20 years. Adding regular deposits raises that figure substantially. Enter your own numbers above to see the exact total.
Does the deposit timing matter? Slightly. Deposits made at the start of each period earn one extra period of interest compared with deposits made at the end, so the start-of-period option gives a marginally higher balance.