Rule of 72 Calculator
Quickly estimate how long money takes to double.
Runs locally in your browser — your numbers never leave this pageTry: Annual rate=8 → 8.00%, 9.0 years
How to use
The rule of 72 is a mental shortcut: divide 72 by the annual percentage rate to get the approximate doubling time. Accurate near 6–10%.
Formula
Years ≈ 72 / r
FAQ
How accurate is it?
Very close for rates between about 4% and 12%; it drifts at very high or very low rates.
Is there a rule of 70 or 69?
Yes. 69.3 is the exact log base, but 72 divides cleanly and is the common version.
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