The Rule of 72

The rule of 72 is a very handy mathematical rule that helps in estimating approximately how many years it will take for an investment to double in value at varying rates of return.

If 72 is divided by an interest rate, the result is the approximate number of years needed to double the investment. For example, at a 10% rate of return, an investment will double in approximately 7.2 years; at a 12% rate of return it will take only 6 years.