Rule of 72 Calculator
Estimate how fast money doubles at any growth rate.
Doubling time (rule of 72)
9 years
Exact doubling time
9.01 years
Quadruples in
18 years
10× in
29.9 years
Compound growth in your head
Divide 72 by the growth rate to get doubling time: 8% doubles money in about 9 years, 6% in 12. It works because ln(2) ≈ 0.693 and 72 is conveniently divisible — accurate within a few percent for rates between 2% and 15%.
It cuts both ways
The rule also measures erosion: 3% inflation halves purchasing power in 24 years; a 12% credit-card... doubles your debt in 6. Any steady percentage — user growth, energy use, fees — obeys the same clock.
Frequently asked questions
- How does the Rule of 72 Calculator work?
- Estimate how fast money doubles at any growth rate.
- Is the Rule of 72 Calculator free to use?
- Yes. The Rule of 72 Calculator is completely free, runs entirely in your browser, and requires no account or sign-up. Your inputs never leave your device.
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