Rule of 72 Calculator
Estimate doubling time using the Rule of 72 and compare it with the exact compound-growth result.
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Rule of 72 estimate
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Exact doubling time
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Approximation difference
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How it works
- The Rule of 72 estimates doubling time by dividing 72 by an annual percentage growth rate.
- The exact mathematical doubling time uses logarithms and assumes a constant annual compound growth rate.
- The Rule of 72 is an approximation and is generally most useful for quick mental estimates.
Rule of 72 Estimate = 72 / Annual Rate (%)
Exact Doubling Time = ln(2) / ln(1 + Annual Rate)
Frequently asked questions
What is the Rule of 72?
It is a quick approximation for estimating how many years a value may take to double at a constant annual percentage growth rate.
Is the Rule of 72 exact?
No. It is an approximation. The calculator also shows the exact mathematical doubling time for comparison.
Does the Rule of 72 guarantee investment returns?
No. It only illustrates the mathematical effect of a constant assumed rate.
Disclaimer
This calculator is for educational illustration only. It assumes a constant growth rate and does not represent or guarantee actual investment performance.