Compound Interest Calculator
See how a balance grows with compound interest and optional monthly deposits. Choose the compounding frequency and the number of years. Free and instant.
Calculate compound interest
How to use the Compound Interest Calculator
- Enter your starting balance and, if you add money regularly, your monthly deposit.
- Enter the annual interest rate and the number of years.
- Choose how often the interest compounds.
- Click Calculate to see the future balance, the interest earned and a year-by-year table.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original balance and the interest already added. Each period’s interest becomes part of the base for the next, so growth speeds up over time.
What is the compound interest formula?
For a single deposit, A = P x (1 + r/n)^(n x t), where P is the principal, r the annual rate as a decimal, n the compounding periods per year and t the years. This calculator also adds monthly deposits.
How does compounding frequency change the result?
More frequent compounding earns slightly more. At 5% for 10 years, monthly compounding ends a little higher than annual compounding, but the rate and the time matter far more.
When are the monthly deposits added?
At the end of each month, after that month’s interest. Depositing at the start of the month would give a slightly higher result.
Does it account for tax, fees or inflation?
No. Real returns vary, and taxes, fees and inflation all reduce them. Treat the result as an illustration, not a forecast.