Rule of 72 Calculator
Estimate how many years it takes for your money to double based on your expected annual return.
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Enter your values and click Calculate to see results.
Learn About the Rule of 72
What is this calculator?
The Rule of 72 is a mental math shortcut investors use to estimate doubling time without a full compound interest calculation.
How does it work?
Divide 72 by your expected annual return percentage. The result approximates the number of years needed to double your investment.
Formula
$$\text{Years to Double} = \frac{72}{\text{Annual Return (\%)}}$$
When should you use it?
- Quick back-of-envelope investment planning
- Comparing growth rates across assets
- Teaching compound growth concepts
Example
At 8% annual return: 72 ÷ 8 = 9 years to double your money. At 12%: 72 ÷ 12 = 6 years.
FAQ
72 has more small divisors (2, 3, 4, 6, 8, 9, 12) making mental math easier. Rule of 70 is also used and slightly more accurate for continuous compounding.
Yes. You can use it to estimate how quickly debt doubles if unpaid, by applying the same formula to the interest rate.