What is the rule of 72 in savings and investments?

The rule of 72 is a quick and very accurate method of determining how long it takes for money to double at a specified rate of interest, compounded annually. For example, using the rule of 72 with a compounded interest rate of 6% it would take 12 years to double your money (72 divided by 6). The precise amount of time it takes to double your money at 6% based on the actual computation of compounded interest is 11.9 years.

The rule of 72 works very well unless the rate of interest exceeds 20% at which point the error rate starts to deviate substantially from the actual answer.

The rule of 72 can also be used to figure out what rate of interest you need to double your money in a specified number of years. For example, if you want to double your money in 5 years, divide 72 by 5 and the interest rate needed is 14.4%.