It is an approximation that works best for moderate rates. Exact doubling time is ln(2)/ln(1+r).

Finance Calculators

Rule of 72 Calculator

Estimate how many years it takes to double money, or required return to double in a target period.

Annual Return Rate (%)

Target Years to Double

Estimated Years to Double9.00

Required Rate for Target Years8.00%

Rule of 72 Formula

Years to Double ≈ 72 / Annual Return%

Required Return% ≈ 72 / Years

At 8% annual return, doubling time ≈ 72/8 = 9 years.

Is Rule of 72 exact?

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