Compound Interest Calculator

Compound interest is interest that earns interest: each period the growth is added to the balance, and the next period's interest is calculated on that larger amount. This compound interest calculator shows what that snowball does to your money — enter the initial principal, the annual rate, how often the interest compounds, and the number of years, and it returns the final balance, the total you contributed and the interest earned on top.

The math is the standard future-value formula FV = P·(1+r/n)^(n·t), where P is the principal, r the annual rate, n the number of compounding periods per year (365 for daily, 12 for monthly, 4 for quarterly, 1 for annual) and t the time in years. If you add a monthly contribution, the calculator assumes it arrives at the end of each month and compounds from that point on at the monthly rate equivalent to your chosen frequency — the same convention banks and most savings calculators use for recurring deposits.

The year-by-year table is where compounding becomes visible. In the early years the balance is driven mostly by your own deposits; further out, the interest column starts growing faster than the contributions column — the crossover point where the account effectively pays in more than you do. The table lists every year up to ten and then every fifth year, so a 30-year projection stays readable.

Everything is calculated locally in your browser: no sign-up, no server, and the amounts work in any currency. Try a few scenarios — a higher rate, an earlier start, a slightly larger monthly deposit — and compare the interest-earned figures to see which lever actually moves your outcome the most.