Compound Interest Calculator
See how an investment or savings balance grows over time with compound interest and optional monthly contributions.
Future value
$124,379.03
$53,000.00 contributed + $71,379.03 in growth
Assumes interest compounds monthly and contributions are made at the end of each month. Actual returns vary.
How the Compound Interest Calculator works
Enter a starting amount, an optional monthly contribution, an expected annual return, and a time horizon. The calculator applies monthly compounding to project your final balance, and breaks it down into what you contributed versus what you earned in growth.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original balance and on interest you've already earned, which is why balances grow faster over longer time horizons.
How often does this calculator compound interest?
Monthly — a common assumption for savings accounts and investment accounts, and a reasonable approximation for most long-term projections.
Why does starting early matter so much?
Because growth compounds on itself, money invested earlier has more time to grow exponentially — even small amounts invested in your 20s can outgrow larger amounts invested later.