Enter Your Principal
Start with your initial investment amount. This is the base on which compound interest will be calculated.
Investment Math
Free Compound Interest Calculator
See the power of compound growth. Enter your principal, interest rate, and time period to calculate your future value with monthly or annual compounding — free, no signup.
Compound Interest
Calculate your investment growth
The compound interest calculator shows how your money grows over time when interest is reinvested.
Set Interest Rate
Enter your expected annual return rate. Historical stock market averages around 7-10% after inflation, but use your own estimate.
Choose Time Period
Set the number of years you'll let your investment grow. Compound interest works best over long time horizons — decades, not months.
The Math
Why compound interest matters
Compound interest is the foundation of long-term wealth building. Here's why it's so powerful.
Exponential Growth
Unlike linear growth, compound interest accelerates over time. The longer you wait, the faster your money grows.
Interest on Interest
Each period, you earn interest not just on your principal but on all previously accumulated interest. This compounds your returns.
Time Is Your Friend
Start early. $10,000 at 7% for 40 years becomes $150,000. The same amount for 20 years becomes only $39,000. Time makes all the difference.
FAQ
Compound interest questions
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. Unlike simple interest (calculated only on principal), compound interest grows exponentially because you earn "interest on interest."
Monthly compounding calculates and adds interest 12 times per year, while annual compounding does it once. More frequent compounding results in slightly higher returns because interest starts earning interest sooner. The difference is small but grows over long time periods.
The compound interest formula is A = P(1 + r/n)^(nt), where A is the future value, P is principal, r is annual interest rate, n is compounding frequency per year, and t is time in years. Our calculator does this math instantly — just enter your values.
Use the Rule of 72: divide 72 by your annual interest rate to estimate doubling time. At 7% returns, your money doubles in about 10 years. At 10%, it takes about 7 years. Our calculator shows exact projections for any rate and time period.
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