Compound interest calculator

This compound interest calculator works out how your savings grow with compound interest and periodic contributions: final balance, amount contributed and interest earned, year by year.

What compound interest is

Compound interest is the mechanism by which your interest, in turn, generates more interest. Instead of being withdrawn, it’s reinvested and becomes part of the capital that keeps growing. Over the long run, this reinvestment makes a huge difference — it’s the force behind the so-called snowball effect.

The formula

Starting from an initial capital C, with periodic contributions A, a rate per period i and n periods, the final balance is:

Balance = C · (1 + i)ⁿ + A · [ (1 + i)ⁿ − 1 ] / i

This tool compounds monthly (monthly rate = annual interest ÷ 12) and adds the contribution at the end of each period.

For guidance only — this is an estimate with a constant interest rate. Real investment returns vary each year and can be negative, and it doesn’t account for inflation, taxes or fees. Not financial advice.