Compound interest calculator
Enter a starting amount, a monthly contribution and an annual rate to see the future value and how much of it is interest.
How to use
- Enter the starting amount, monthly contribution, annual interest rate and number of years.
- Choose how often interest compounds and whether you contribute at the start or end of each month.
- Read the final balance, total contributions and interest earned, plus the yearly chart and table.
Compound interest calculator
Compound interest means interest is added to the balance and then earns interest itself. With a starting amount P, rate r and n compounding periods per year, the balance after t years is P × (1 + r/n)^(n·t). Monthly contributions are added each month; when interest compounds other than monthly, the calculator uses the equivalent monthly rate so contributions and compounding stay consistent.
The effective annual rate shows what the stated rate is worth after compounding — 12% compounded monthly is about 12.68% a year. Results are estimates with a fixed rate and no taxes, fees or inflation; real investment returns vary and can be negative. This is not financial advice.
Frequently asked questions
What is the difference between contributing at the start or end of the month?
Contributions at the start of the month earn one extra month of interest each time, so the final balance is slightly higher.
Does it include inflation or taxes?
No. Enter a rate after fees if you want a more conservative estimate, and remember the result is in today's currency without inflation.
Which currency does it use?
Any currency — the results use the same unit you enter.