About this tool
Use the Rule of 72 to estimate how long an investment takes to double at a given rate, or the rate needed to double in a given time. Edit either field and the other updates live in your browser.
Frequently asked questions
How accurate is the Rule of 72?
It is a quick approximation that works best for rates roughly between 6% and 10%; for very high or low rates the exact doubling time drifts a little from 72 ÷ rate.
How do the two fields relate?
They are two views of the same rule: years to double = 72 ÷ rate, and the required rate = 72 ÷ years, so changing one recalculates the other.