Using the Rule of 72 how long will it take for a deposit to double in size using an interest of 9?

The Rule of 72 is a simple formula to estimate the number of years required to double an investment at a fixed annual interest rate. To find out how long it will take for a deposit to double at an interest rate of 9%, you divide 72 by 9. This calculation gives you approximately 8 years for the deposit to double in size.