How to use the compound interest calculator
Enter your starting amount, the annual interest rate, and how many years you plan to invest. Choose how often interest compounds, and if you add money regularly, enter the contribution per period. The calculator shows the future value, how much you contributed in total, and how much of the growth came from interest alone.
Why compounding is called the eighth wonder
The power of compound interest is that growth builds on growth. In the early years the interest is modest, but because each year’s gains are added to the balance and then earn their own interest, the curve steepens over time. Doubling the number of years usually far more than doubles the final amount — which is why time in the market is the single most valuable ingredient.
Contributions versus lump sums
A one-off deposit grows steadily, but adding a regular contribution changes the picture entirely. Each new contribution starts its own compounding journey, and the earliest ones have the longest to grow. The tool separates your total contributions from the interest earned so you can see exactly how much of your final balance the market did for you. These figures are projections at a constant rate; real returns vary year to year.