Rule of 72 Calculator
Estimate how many years it takes for money to double at a given interest rate.
Quick answer: enter your details below and click Calculate — your result appears instantly, right here in your browser. Nothing you enter is uploaded or stored.
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Calculators
Enter your details below.
How to use
- Enter the annual interest rate as a percentage.
- Press Calculate to see the estimated years to double.
- Try different rates to see how doubling time changes.
About this tool
This calculator uses the rule of 72, a handy shortcut for doubling time: years to double = 72 divided by the annual interest rate in percent. It is an approximation that works well for typical rates, and it also shows the same answer in months. A higher rate means a shorter doubling time.
Frequently asked questions
Why 72?
Because 72 is easy to divide by many common rates, and it gives a close approximation to the exact doubling time for rates in the usual range.
Is the answer exact?
No, it is an estimate. The exact doubling time depends on compounding, but the rule of 72 is close enough for quick planning at ordinary rates.