Doubling Time Calculator
Find how many periods a quantity needs to double at a constant positive growth rate.
Formula
t = ln(2) / ln(1 + r/100)
Doubling time (periods) ≈ ln(2)÷log1p((10)÷100)
How to use
- Enter the effective percentage growth per period.
- Use one consistent period, such as a year.
- Read the doubling time in those periods.
Examples
- 100% per period doubles in 1 period; 25% takes about 3.106284 periods.
Frequently asked questions
Does the starting amount matter?
No. It cancels when solving N(1+r/100)^t=2N.
Is this the rule of 72?
No. This uses the logarithmic formula for fixed compound growth.
Can the rate be zero or negative?
No. Such a quantity does not double by positive growth under this model.
Sources
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