Compound Interest Calculator
See how a lump sum and monthly contributions grow with compound interest, with a year-by-year table, a chart and the rule of 72.
Results
Enter an amount, rate and period to see the final balance and how it grows each year.
How to use
- Enter the initial amount, the annual interest rate (or expected annual return) and the number of years.
- Choose how often interest compounds: yearly, half-yearly, quarterly or monthly.
- For regular saving, enter a monthly contribution and whether it goes in at the start or end of each month.
- You get the final balance, total contributions and interest earned, plus a year-by-year chart and table.
FAQ
What is the compound interest formula?
For a lump sum, final balance = principal × (1 + rate ÷ n)^(n × years), where n is how many times a year interest compounds. 10,000 at 5% compounded monthly for 10 years grows to about 16,470; compounded yearly, about 16,289.
How are monthly contributions handled?
The tool works month by month: interest accrues at the annual rate ÷ 12 and is added to the balance at the end of each compounding period. Money added at the start of a month earns interest that month; money added at the end starts the next month. With monthly compounding this matches the future value of an annuity formula.
What is the rule of 72?
Divide 72 by the annual rate in percent to estimate how many years it takes to double your money: about 12 years at 6%. It is an approximation that gets worse at high rates, so the tool also shows the exact doubling time for the chosen compounding.
What is the effective annual rate?
It is the actual growth over one year once compounding is counted: (1 + rate ÷ n)^n − 1. A 12% rate compounded monthly is about 12.68% a year.
Can I use this to predict investment returns?
The calculation assumes a fixed rate and ignores taxes, fees and inflation. Returns on stocks and funds vary from year to year, so treat the result as an illustration, not a forecast.
Is my data uploaded?
No. Everything is calculated in your browser, with no network connection needed.
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