Rule of 72
Estimate how many years it takes to double your money.
About Rule of 72
The rule of 72 approximates doubling time by dividing 72 by the annual rate of return. At 8 percent, money doubles in about nine years. It is a fast mental shortcut for comparing investments and appreciating just how powerful compounding is.
Formula
Rule of 72
Years to double = 72 / r
- r
- annual rate of return in percent
Worked example
With the default values below, Rule of 72 returns Years to Double of 9.00. Change any input above and every figure here is recalculated in your browser.
Inputs used
- Annual rate of returnaccepts 0.01–100 %
- 8 %
Results
- Years to Double
- 9.00
- Months to Double
- 108
- Days to Double
- 3,287
Step by step
- 1Values used
- 2Rule of 72
- 3Years to Double= 9.00
- 4Months to Double= 108
- 5Days to Double= 3,287
Assumptions and limits
- The result is derived only from the single input listed above. Anything not among them is not part of the calculation.
- In particular, this calculator does not take inflation, tax or fees or charges into account.
- Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.
- This is an estimate for general information and not professional financial, tax or legal advice. See the full disclaimer for the limits that apply to this kind of calculator.
How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.
Frequently Asked Questions
How is Rule of 72 calculated?
Years to double = 72 / r The rule of 72 approximates doubling time by dividing 72 by the annual rate of return. At 8 percent, money doubles in about nine years.
Why does Rule of 72 matter?
It is a fast mental shortcut for comparing investments and appreciating just how powerful compounding is.
What values do I need to enter?
This calculator takes 1 input: Annual rate of return. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.