Rule of 72 Calculator
Estimate how many years it takes to double your money at a given interest rate.
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How to do it
- 1Fill in the boxes
Type your numbers or pick the options you need.
- 2See the result
The answer updates right away as you change a value.
- 3Use it
Copy the result or note it down. Nothing is sent anywhere.
About this tool
Enter an annual rate of return. The rule of 72 divides 72 by the rate to estimate the years to double. The tool also shows the exact result, and the rule of 114 and 144 for tripling and quadrupling.
The rule
Divide 72 by the interest rate to get the approximate years for money to double with compound interest. At 6 percent it takes about 12 years, at 9 percent about 8 years. It is accurate for rates between about 4 and 12 percent.
Why it matters
It shows how rates and time compound. It also works for inflation: at 3 percent inflation prices double in about 24 years.
Other versions
Use 114 for tripling and 144 for quadrupling. For very high or low rates, the exact formula is shown for comparison.
Frequently asked questions
Is it exact?
No, it is an approximation. The exact figure uses logarithms and is shown below the estimate.
Does it work for inflation?
Yes. Divide 72 by the inflation rate to see when prices double.
Why 72?
72 has many divisors and gives a good fit to the exact formula at typical rates.
Does it include contributions?
No. It assumes a single amount that compounds.