Compound Interest Calculator
Calculate compound interest on savings and investments. See how your money grows over time with monthly contributions.
View Year-by-Year Growth
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What Is Compound Interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (calculated only on the principal), compound interest causes your money to grow exponentially over time. Albert Einstein reportedly called it "the eighth wonder of the world."
How This Calculator Works
Enter your initial investment, monthly contribution, annual interest rate, and time period. The calculator shows your total future value, how much came from contributions vs. interest, and a year-by-year breakdown of growth. All processing is done in your browser.
The Power of Starting Early
Starting to invest even small amounts early makes an enormous difference due to compound interest. Investing $200/month at 7% annual return from age 25 to 65 yields about $525,000 — but starting at 35 yields only about $244,000. That 10-year head start nearly doubles the result, even though you only contributed $24,000 more.