Rule of 72 Calculator
Estimate how many years it takes to double money at a given yearly return, using the rule of 72 and the exact formula.
- Years to double (exact)
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- Difference
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An estimate only; it assumes steady compounding.
What is the Rule of 72 Calculator?
This rule of 72 calculator estimates how many years an amount takes to double at a yearly return you enter. It shows the quick rule-of-72 answer, the exact answer from the compound growth formula and the gap between them, so you can see how close the shortcut is.
How it works
The rule of 72 divides 72 by the yearly rate in per cent to estimate the doubling time in years. The exact figure is ln 2 divided by ln (1 + r), where r is the yearly rate as a fraction. A rate of zero or below never doubles, so the result shows zero.
How to use it
- Enter the yearly return in per cent.
- Read the doubling time from the rule of 72.
- Compare it with the exact doubling time.
- Try other rates to see how doubling time changes.
Rule of 72 Calculator — FAQ
Why 72?
It is a convenient number that divides evenly by many common rates and gives a close estimate of doubling time for moderate rates.
How accurate is the rule?
It is close for everyday rates and drifts for very low or very high rates. The exact figure shown here is more precise.
Can I use it for inflation?
Yes. Enter the inflation rate to estimate how many years it takes for prices, or costs, to double.