Rule of 72
Years to double an investment at a given rate — approx vs exact.
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About Rule of 72
Estimate years to double money at a given rate — rule of 72 versus exact ln math.
Approx years = 72 / rate%. Exact = ln(2)/ln(1+r). Both shown so you can see the error band.
How to use Rule of 72
- 1Enter annual return %.
- 2Compare approximate and exact doubling times.
Common questions
When is the rule accurate?
Best around mid-single-digit rates; diverge more at extremes.
Related tools
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