Doubling Time Calculator (Rule of 72)
How long money takes to double at a given rate, exactly and by the rule of 72.
Results
Years
11.896
Years
12.000
Percentage change
79.08
%
What this tool does
The rule of 72 is the mental shortcut: divide 72 by the percentage rate and you get the doubling time in years. This shows the exact logarithmic answer next to it, so you can see how close the shortcut really is — remarkably close for rates between 4 % and 12 %.
Formula
t = ln 2 ÷ ln(1 + i) · rule of 72: t ≈ 72 ÷ i
Variables
| Symbol | Meaning | Unit |
|---|---|---|
r | Annual interest rate | % |
T | Years | — |
T72 | Years | — |
T10 | Percentage change | % |
Worked example
- Annual interest rate6 %
- Years11.896
- Years12.000
- Percentage change79.08 %
Limitations
- This is an informational calculator, not personalised financial advice. Rates, fees, taxes and contract conditions vary between institutions and countries.