How to use this calculator
Enter your starting principal, the expected annual interest rate, the number of years you plan to stay invested, and how often interest compounds. The tool shows the projected future value and how much of that is interest earned versus your original investment.
How compound interest works
Compound interest is calculated with A = P × (1 + r/m)^(m×t), where P is the principal, r is the annual rate, m is the number of compounding periods per year, and t is the number of years. Because each period earns interest on the previous interest, growth accelerates over time, the longer you stay invested, the more dramatic the effect.
Why time matters most
The single biggest driver of compound growth is time. $10,000 at 8% becomes about $21,600 in 10 years, but roughly $46,600 in 20 years, more than double, for only twice the wait. Starting early beats investing larger amounts later.