Rule of 72 Calculator
Compare the quick doubling-time estimate with exact annual compounding.
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Use consistent units and periods. Defaults are examples.
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Check the assumptions below before relying on a result.
Formula and method
Rule of 72 years = 72 ÷ annual percentage rate. Exact annual-compounding time = ln(2) ÷ ln(1 + rate ÷ 100).
Worked example
At 8% annual growth the Rule of 72 estimates nine years. The exact continuous time along the annual-compounding curve is about 9.006 years; at whole year ends the balance first doubles after 10 years.
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