by David Jenyns on June 5, 2011

Question by Finance F: Finance?????
The “Rule of 72” suggests that an amount will double in 12 years at a 6 percent compound annual rate or double in 6 years at a 12 percent annual rate. Is this a useful rule, and is it an accurate one?

Best answer:

Answer by mule
Have you always wanted to be able to do compound interest problems in your head? Probably not, but it’s a very useful skill to have because it gives you a lightning fast benchmark to determine how good (or not so good) a potential investment is likely to be.

The rule says that to find the number of years required to double your money at a given interest rate, you just divide the interest rate into 72. For example, if you want to know how long it will take to double your money at eight percent interest, divide 8 into 72 and get 9 years.

Yes, it is a useful tool and is reasonably accurate.

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