The first term compounds your starting principal P; the second is the future value of regular contributions PMT. r is the annual rate, n the number of compounds per year, and t the years. Compounding more frequently and starting earlier both raise the result — time is the biggest lever.
How compound interest works
Compound interest is the engine behind long-term saving and investing: you earn interest on your principal and on the interest already earned. The longer the time horizon, the more dramatic the effect — which is why starting early matters more than starting big.
This calculator compounds monthly and lets you add a recurring monthly contribution. Drag any slider to see how rate, time, and contributions each reshape your future value and the split between what you put in and what the interest earned for you.
For information only; not financial advice. Real returns vary and are not guaranteed.