The rule of 72 is a way of finding out long it will take for your investment to double. Divide an investment’s annual return into 72, and you will have the number of years necessary to double your investment.
Example: An investment’s annual return is 10 percent. Ten percent divided into 72 is 7.2, so your investment will double in 7.2 year.
bonds fluctuate in price, there can be a large difference between yield and total return.