Project how an initial deposit plus regular contributions grows over time with compound interest. Compare compounding frequencies and see how much of your final balance comes from interest rather than your own deposits.
How to use the Compound Interest Calculator
- Enter your starting balance.
- Enter your regular monthly contribution (optional).
- Enter the expected annual interest rate or return and the number of years.
- Choose the compounding frequency and review the final balance and year-by-year table.
Compound interest formula
Future value of a lump sum: A = P(1 + r/n)^(n·t), where P is the principal, r the annual rate, n the compounding periods per year and t the number of years.
Regular monthly contributions are added each month and grow at the equivalent monthly rate. The calculator simulates every month so different compounding frequencies are handled precisely.
The power of time
Because interest earns interest, growth accelerates over time. Starting ten years earlier can matter more than doubling your contribution — adjust the years to see it.
Frequently asked questions
What is the difference between simple and compound interest?
Simple interest is paid only on the original amount. Compound interest is paid on the original amount plus previously earned interest, so it grows faster.
What is the rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes to double your money. At 8% that is about 9 years.
Does this include inflation or taxes?
No. To see real growth, subtract the expected inflation rate from your return rate.