Free Rule of 72 Calculator
Estimate how long it takes to double your money at a given interest rate using the Rule of 72.
%
Years to Double
9.0
Exact Years (ln2/r)9.01
Years to Double vs Annual Interest Rate
The Rule of 72
Years to Double ≈ 72 / Interest Rate
This is an approximation. The exact formula is:
Years = ln(2) / ln(1 + r)
The Rule of 72 is most accurate for rates between 6% and 10%.
Example Calculation
Your investment earns 8% annually.
- 01Rule of 72: 72 / 8 = 9.0 years
- 02Exact: ln(2) / ln(1.08) = 0.6931 / 0.07696 = 9.01 years
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