About the Compound Interest Calculator
Compound interest means you earn interest on your interest — the longer you save, the faster your money grows. Enter a starting amount, regular monthly contributions, an interest rate and a time period to see your future balance.
The year-by-year table shows exactly how much comes from your contributions and how much from interest.
How to use the Compound Interest Calculator
- Enter your starting amount.
- Enter how much you will add each month (or 0).
- Enter the yearly interest rate and the number of years.
- Choose how often interest compounds.
Frequently asked questions
What is the compound interest formula?
A = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate, n the number of compounding periods per year and t the number of years. Regular contributions are added on top.
What is the Rule of 72?
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 8%, money doubles in about 9 years.
Does compounding frequency matter much?
More frequent compounding earns slightly more, but the interest rate and the time you stay invested matter far more.