Compound Interest Calculator

See how your money grows over time. Enter a starting amount, optional monthly contributions, an annual interest rate and a number of years to get the future value, the total interest earned, and a year-by-year breakdown. Updates as you type. Runs in your browser — no signup.

How compound interest works

Compound interest means you earn interest on your interest, not just on the money you put in. Each period the balance grows, and the next period's interest is calculated on that larger balance — so growth accelerates the longer you leave it. That snowball effect is why starting early matters far more than starting big.

• Starting amount — what you have invested today.
• Monthly contribution — what you add each month (set to 0 for a one-time deposit).
• Rate — the expected annual return. A broad stock-market index has historically averaged roughly 7% after inflation, but returns are never guaranteed.
• Compounding — how often interest is added back to the balance.

This is an educational estimate, not financial advice. Real returns vary and aren't guaranteed.

FAQ

How is compound interest calculated?

You earn interest on your balance, then the next period you earn interest on that larger balance too. This calculator compounds each month using a rate equivalent to your chosen annual rate and compounding frequency, adding any monthly contribution along the way, so growth accelerates over time.

What interest rate should I use?

Use the expected annual return for where the money sits. Savings accounts are often low single digits; a broad stock-market index has historically averaged roughly 7% a year after inflation, but returns are never guaranteed. Try a range to see best and worst cases.

Does the calculator include monthly contributions?

Yes. Set a monthly contribution to model regular saving, or leave it at 0 for a one-time deposit. The result shows the future value, how much you put in, and the interest earned on top.

Is this financial advice?

No. It is an educational estimate only. Real returns vary, are not guaranteed, and do not account for tax or fees. Speak to a qualified professional about your situation.

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