Rule of 72 Calculator
Quickly estimate how many years it takes an investment to double at a given rate, using the Rule of 72 shortcut.
Rule of 72
Doubling time
Years to double
9.0 years
at 8% p.a.
Frequently asked questions
The Rule of 72 is a quick mental-math shortcut for estimating how many years it takes an investment to double at a given annual compound return. Divide 72 by the return rate to get the approximate number of years.
It is an approximation, not an exact calculation. It works best for annual return rates between roughly 6% and 10%, where the error stays under a few percent. Outside that range, the approximation drifts further from the true doubling time.
Use the Compound Interest Calculator for a precise answer, since it applies the exact compound interest formula rather than the Rule of 72 shortcut.
Yes, if you know how many years you want your money to double in, divide 72 by that number of years to estimate the annual return rate you would need. This calculator supports both directions.
Yes, the same shortcut applies to any quantity that grows at a steady compounding rate, such as inflation eroding purchasing power or a loan balance growing at a fixed interest rate. The math is identical either way.
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The Rule of 72 is an approximation, most accurate for rates between 6% and 10%. For a precise doubling time at any rate, use the Compound Interest Calculator.