Compound Interest Calculator

How compound interest changes your money over time

Compound interest is the process of earning interest on both your original deposit and the interest that has already been added to the balance. This calculator models that effect with a starting deposit, a monthly contribution, an annual rate, a time period, and a compounding frequency. The result is not a guarantee, but it gives you a practical way to compare scenarios before you save, invest, or adjust a recurring contribution.

The most important inputs are usually time and contribution consistency. A higher annual return can help, but more years in the market give compounding more room to work. The chart separates deposits from interest so you can see when growth starts coming less from new money and more from accumulated earnings. The donut chart shows the final split, while the yearly interest chart highlights how annual earnings can accelerate as the balance grows.

For planning, try changing only one input at a time. Increase the monthly contribution, then compare the final balance. Move the time period from 10 years to 20 years and watch how the later years carry more of the growth. If you are comparing account options, use the compounding frequency control to understand whether annual, quarterly, monthly, or daily compounding materially changes the projection for your assumptions.