Compound Interest Calculator
See how an investment grows over time with compounding.
Educational estimate. Real returns vary and are not guaranteed. Not investment advice.
About Compound Interest Calculator
Compound Interest Calculator models how an investment grows when returns are reinvested. Compounding is what makes long-term saving and investing work: each period's earnings start earning their own returns the next period, and over decades the difference becomes dramatic. The calculator takes a starting deposit, an optional regular contribution, an expected annual rate, a compounding frequency, and a time horizon, then shows the year-by-year balance.
Worked example: start with $5,000, add $500 a month, assume 7% annual return compounded monthly, hold for 20 years. The calculator shows a final balance around $280,700 — of which exactly $125,000 is your own contributions and about $155,700 is growth. Year by year you can see when growth starts outpacing contributions, which is the moment compounding really starts to take over.
The frequency choice matters less than the rate or the time horizon, but it is not negligible — at 7% over 20 years, monthly compounding beats annual by roughly 4% of the final balance — so pick the option that matches your account (most savings accounts and index funds effectively compound monthly or daily). The much bigger levers are the rate, the time horizon, and the contribution amount. What this calculator deliberately does not model: taxes, inflation, fees, or rate volatility. Real returns are not constant — they jump and dip — so treat the output as an illustrative projection, not a forecast.
All numbers stay in your browser. Nothing about your savings goals, balances, or income is logged or uploaded.