Compound Interest Calculator
Estimate the future value of your savings or investments, including regular monthly contributions and the effect of compounding.
How compound interest works
Compound interest is interest earned on both your original principal and the interest it has already generated. Because each period builds on the last, growth accelerates over time — the effect Einstein is often (apocryphally) said to have called the eighth wonder of the world.
The formula
The future value of a lump sum with regular contributions is FV = P(1+i)ⁿ + PMT·((1+i)ⁿ−1)/i, where i is the rate per period and n is the number of periods. This calculator applies it for you and separates how much you contributed from how much was pure growth.
Getting the most from compounding
Two levers matter most: time and consistency. Starting five years earlier often beats contributing more later, and automating a fixed monthly amount removes the temptation to skip. Small differences in annual rate also widen dramatically over decades.