Rule of 72 Calculator
Find out how many years it takes to double your money at a given return rate.
Years to Double (Rule of 72)
0.0 years
Exact Doubling Time
0.00 years
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What is the Rule of 72?
The Rule of 72 is a quick mental shortcut for estimating how long an investment takes to double: divide 72 by the expected annual return rate. At 12% annual returns, money roughly doubles every 6 years (72 ÷ 12).
This calculator shows both the Rule of 72 approximation and the exact doubling time using the precise logarithmic formula, so you can see how close the shortcut gets at your chosen return rate — it stays quite accurate between roughly 6% and 12%, and drifts slightly outside that range.
The same shortcut works in reverse for inflation: dividing 72 by an inflation rate estimates how long it takes prices — or the purchasing power of idle cash — to effectively double or halve. It's a handy way to sanity-check both investment growth and inflation erosion in your head without reaching for a full calculator.