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Rule of 72 Calculator

Estimate how many years it takes an investment to double at a given rate.

Inputs

%
%

Saved Scenarios

— select 2+ to compare

Years to Double

9.0

Spark says

How it's calculated

Formula

Years≈72RateYears \approx \dfrac{72}{Rate}
Rate
— Annual growth rate (%)

What is the Rule of 72 Calculator?

The Rule of 72 is a quick mental-math shortcut for estimating how long it takes an investment to double, by dividing 72 by the annual growth rate.

How to use it

  1. 1 Enter the expected annual growth rate.

Worked examples

8% annual return

Doubles in about 9 years.

Try it

Limitations

  • •An approximation — it's most accurate for rates between about 6% and 10%; for precise figures, use the Compound Interest calculator directly.

Frequently asked questions

How accurate is the Rule of 72?

Very close for typical investment rates (6-10%), with small deviations outside that range. For exact figures, use logarithms or the Compound Interest calculator.