Compound Interest Calculator
See how your money grows over time when interest compounds. Enter a starting amount, an annual interest rate, the number of years, how often interest compounds and any regular monthly contribution, and the calculator projects your future balance and the total interest earned.
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Last reviewed January 15, 2026.
Method: Future value = P(1 + r/n)^(nt) plus the future value of any regular contributions, compounded at the frequency you select.
How it works
The compound interest formula for a lump sum is:
A = P × (1 + r ÷ n)n × t
where A is the final amount, P is the principal, r is the annual rate, n is the number of compounding periods per year and t is the number of years. When you add regular monthly contributions, each deposit also earns compound interest for the remaining time.