Doubling time calculator
Estimate how long a quantity takes to double at a constant growth rate.
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Tool guide
Doubling time calculator: how it works
Practical information to understand the result and use this tool correctly.
About Doubling time calculator
Doubling time asks how many periods until a quantity multiplies by two at a steady percent rate.
The exact formula uses natural logs; the rule of 72 is a fast mental estimate shown alongside.
The period unit must match how the rate was measured (per year, per month, etc.).
How to use it
- 1Enter growth rate as percent per period.
- 2Calculate periods to double.
- 3Compare with the rule-of-72 approximation.
Frequently asked questions
- Rule of 72 accuracy?
- It is close for mid-single-digit rates; this tool’s log formula is exact under constant growth.
- Negative rates?
- Decline has no doubling time — the rate must be positive.