About this tool
Final balance and interest earned with compound growth.
Compound interest means earning interest on both the original principal and the accumulated interest from previous periods, causing the balance to grow exponentially over time. The Compound Interest Calculator shows the final balance and total interest earned for any principal, annual rate, compounding frequency, and time period. The classic Rule of 72 — dividing 72 by the annual interest rate — gives a quick mental estimate of how many years are needed to double your money.
Example
$1,000 at 7% for 10 years (annual compounding) → $1,967.15 · Interest earned: $967.15
How to use
- Enter the starting principal (initial investment).
- Enter the annual interest rate as a percentage.
- Choose the compounding frequency: annual, quarterly, monthly or daily.
- Enter the investment period in years to see the final balance.
Features
- Final balance and total interest earned
- Multiple compounding frequencies (annual / quarterly / monthly / daily)
- Year-by-year balance growth table
- Rule of 72 doubling-time estimate
- Supports any currency or unit of money
Frequently Asked Questions
What is compound interest?+
Compound interest is interest calculated on the initial principal plus all previously accumulated interest. The formula is A = P(1 + r/n)^(nt), where n is compounding periods per year.
How often should interest compound?+
More frequent compounding produces marginally higher returns. Daily compounding yields slightly more than monthly, which yields slightly more than annual, for the same nominal rate.
What is the Rule of 72?+
Divide 72 by the annual interest rate to estimate doubling time. At 6% the investment doubles in about 72 ÷ 6 = 12 years. At 9% it doubles in about 8 years.
Does this account for inflation?+
No — the result is the nominal (before-inflation) growth. To find real returns, subtract the expected inflation rate from the interest rate before calculating.
What compounding frequency gives the most growth?+
More frequent compounding = more growth: daily > monthly > annually. The difference shrinks at very high frequencies.
What is the Rule of 72?+
Divide 72 by the annual rate to estimate doubling time. At 7%: 72 ÷ 7 ≈ 10.3 years.