How the Rule of 72 Calculator works
Estimate how long money may take to double. Adjust the inputs above, then use the calculate button to generate a fresh estimate based on the numbers you entered.
The result is designed to give you a quick planning number, plus a short breakdown of the major figures behind it. You can reset the form at any time and try a different scenario.
When to use this calculator
Use this Rule of 72 calculator for a quick estimate of how long money may take to double at a given annual return. It is a mental-math shortcut, not a precise investment projection.
Formula
Years to double = 72 / annual return percentage
- Annual return is the growth rate used in the estimate.
- The result estimates the number of years needed for money to double.
- The shortcut works best for moderate positive return rates.
Worked example
At a 6% annual return, the Rule of 72 estimates money may double in about 12 years.
Common mistakes
- Treating the shortcut as exact for every return rate.
- Using it for volatile investments without considering risk.
- Ignoring fees, taxes and inflation.
FAQs
Why 72?
72 is a convenient approximation that works reasonably well for common growth rates.
Can I use it for inflation?
Yes. It can estimate how long prices may take to double at a steady inflation rate.
Does doubling mean buying power doubles?
Not necessarily. Inflation can reduce the buying power of future dollars.