Compound Interest Calculator
See how your savings grow when interest earns interest. Add regular contributions, choose how often interest compounds and review every year.
How to calculate compound interest
- Enter your starting amount, monthly contribution and expected annual interest rate.
- Set the number of years and how often interest compounds.
- Read the future value, how much you contributed versus earned, and the year-by-year table.
Features
Regular contributions
Include monthly deposits at the start or end of the month.
Year-by-year table
Watch the balance and interest build each year.
Effective yield
See the real annual rate after compounding.
Private
Everything is calculated in your browser; nothing is sent anywhere.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original money and on the interest already added. Over long periods this snowball effect makes growth accelerate.
What is the compound interest formula?
A = P(1 + r/n)^(nt) for a lump sum, where P is the principal, r the annual rate, n the compounding periods per year and t the years. With contributions, the calculator applies the periodic rate month by month.
Does compounding frequency matter much?
A little. More frequent compounding gives slightly more interest, but the rate and the time matter far more. Daily versus monthly on 7% differs by only a few hundredths of a percent a year.
Are returns guaranteed?
No. Real investments vary and may lose value. This calculator assumes a steady rate and ignores fees, taxes and inflation, so treat it as an illustration.