Rule of 72 Calculator
Estimate how long it may take money to double at a fixed return rate.
How this calculator works
How to use this calculator
1. Enter an annual return rate greater than 0.
2. Click Calculate Years to Double.
3. The calculator divides 72 by the rate to estimate how many years doubling may take.
Formula used
Estimated Years to Double = 72 ÷ Annual Return Rate (%)
The Rule of 72 is a shortcut approximation rather than an exact compounding formula.
Example calculation
Example: 8% annual return
Years to Double = 72 ÷ 8
Years to Double = 9 years
What the result means
The result is a quick estimate of how long money may take to double at a constant annual rate. Because the Rule of 72 is an approximation, the exact doubling time may differ.
Frequently asked questions
Is the Rule of 72 exact?
No. It is a mental-math approximation that is reasonably useful for many common rates.
Can I use a 0% or negative rate?
No. This calculator requires a positive annual rate because money does not double under a zero or negative constant return.
Does this include contributions?
No. It estimates doubling of an existing amount based only on the entered rate.