Free Rule of 72 Calculator - Calculate Investment Doubling Time
Quickly estimate how long it takes for an investment to double, or what interest rate is needed to double your money.
Formula & Methodology
A highly accurate mathematical shortcut for estimating the effect of compound interest without complex logarithmic equations.
- Years to Double = 72 / Interest Rate
- Required Rate = 72 / Years to Double
Worked Example
Using the Rule of 72 Calculator: apply the formula above to your input values. For instance, Years to Double = 72 / Interest Rate, then Required Rate = 72 / Years to Double. The tool performs each step instantly and shows the result.
Frequently Asked Questions
What is the Rule of 72?
A quick shortcut: divide 72 by your annual return rate to estimate how many years it takes your money to double.
How accurate is the Rule of 72?
It is a close approximation for rates between about 6% and 10%; outside that range it drifts slightly from the exact figure.
Can I use it to find a required rate?
Yes. Divide 72 by the years you want, and the result is the annual return needed to double your money in that time.