Rule of 72 Calculator
Compare the Rule of 72 doubling-time estimate with the annual compound-growth equation.
Formula
Approximate years = 72 / annual%; compound years = ln(2) / ln(1 + annual%/100).
Rule of 72 years ≈ 72÷(8) · Annual-compounding years ≈ ln(2)÷log1p((8)÷100)
How to use
- Enter a positive annual return.
- Read the Rule of 72 estimate.
- Compare with the compound-growth result.
Examples
- At 8%: the Rule of 72 gives 9 years; annual compounding gives about 9.01 years.
Frequently asked questions
Is the Rule of 72 exact?
No. It is a quick approximation; the difference can be large at extreme rates.
Are returns guaranteed?
No. Both results assume your positive return stays constant.
What about fees and taxes?
They are excluded; neither result predicts investment performance.
Sources
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