Stocks do not have a fixed rate of return, so you cannot directly use the Rule of 72 to determine how long it will take to double your money. However, you can use it to estimate the average annual return required to double your money within a specific time frame. To do this, divide 72 by the number of years you want to take to double your money. For example, if you want to double your money in eight years, divide 72 by eight, which results in an average annual return of 9%.