Compound Interest Calculator
Project growth with compound interest.
Interest earning interest
Compound interest grows on both principal and prior interest, following A = P(1 + r/n)^(nt). $10,000 at 7% compounded yearly becomes about $19,700 in ten years — the effect that makes early investing powerful.
Compounding frequency matters too — monthly compounding beats annual at the same rate — and contributing regularly rather than a lump sum changes the curve dramatically over decades.
A projection, not a promise
Real returns vary and are rarely constant, so treat this as illustrative. Your figures stay in the browser and are never uploaded.
Frequently asked questions
How often does interest compound?
Monthly. Each month the balance grows by the annual rate ÷ 12, then that month's contribution is added. $10,000 plus $500 a month at 7% for 20 years grows to about $300,851.
What goes in the "Annual rate %, years" box?
Two comma-separated numbers: the annual return, then the number of years. "7, 20" means 7% a year for 20 years.
Does it account for inflation or taxes?
No. The result is in future dollars before tax. To see today's buying power, subtract expected inflation from the rate, for example using 4% instead of 7%.
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