What is the rule of 72 used for in interest calculations?

The rule of 72 is a simple way to estimate how long it will take for an investment to double in value at a given annual interest rate. The rule states that the time (in years) required to double an investment is approximately 72 divided by the annual interest rate. For example, if the interest rate is 6%, the time to double is around 72/6 = 12 years. This rule provides a quick, rough estimate useful for basic interest calculations. It is derived from the properties of exponential growth and continuous compounding.