The rule of 72 is a quick mental calculation you can use to calculate the years or compounding investment returns % to double a sum of money.

the-rule-of-72

Calculate Years to Double Your Money at 8% Compounding Returns
Years to Double Your Money
= 72 / 8
= 9 years

Calculate Investment Returns % to Double Your Money over 3 years
Compounding Investment Returns %
= 72 / 3
= 24%

This formula is useful for calculating either time or rate of returns to double your money.