Free Compound Interest Calculator: See What Your Money Could Grow To
Enter a starting amount, a monthly contribution, an expected annual return, and a time horizon to see how compound growth adds up. This is a planning tool, not a prediction — real returns vary year to year.
How this calculator works
The calculator compounds monthly: each month, your balance earns a share of the annual return you entered, and then your monthly contribution is added on top. Over enough years, the interest your money earns starts generating more growth than your original contributions did — that acceleration is what "compound interest" actually means, and it's the reason starting early matters more than starting with a large amount.
What return rate should you use?
A broad stock market index fund has historically averaged roughly 7% per year after adjusting for inflation over long periods, though any single year can be sharply higher or lower. A high-yield savings account or CD will show a much lower, more stable number reflecting current interest rates. Try running the calculator at a couple of different rates (say 4% and 8%) to see the realistic range of outcomes rather than anchoring to a single optimistic number.
What to do with your number
If the result looks smaller than you'd like, the two levers that move it most are the monthly contribution and the number of years — both matter more than chasing a slightly higher return rate. If you haven't started investing yet, our guide to investing your first $100 walks through exactly how to open an account and put a plan like this into action.
Once you've started investing based on these numbers, our Investment Portfolio Tracker is the natural next step for keeping tabs on how the real thing compares to the projection.
Disclaimer: This calculator is for educational and illustrative purposes only and does not constitute financial advice. It assumes a constant rate of return, which real investments do not provide — actual results will vary and may include losses. Please read our full Disclaimer before acting on anything you read here.
