A way to **estimate** how long it takes to double the value of an investment.

You divide 72 by the interest rate to get the number of years.

Examples:

• For an annual rate of 8%, divide 72 by 8, for a result of 9 years. So at 8% it takes about 9 years to double your money.

• For an annual rate of 10%, divide 72 by 10, for a result of 7.2 years. So at 10% it takes about 7 years to double your money.

But it is only an estimate, and there are more exact formulas.