The Rule of 72 predicts how long an investment will take to double based on a fixed annual interest rate. The rule is this: 72 divided by the interest rate number equals the number of years for the investment to double in size. For example, if the interest rate is 12%, you would divide 72 by 12 to get 6. This means that the investment will take about 6 years to double with a 12% fixed annual interest rate. Enter a fixed annual interest rate into the calculator to see how long it will take for the investment to double in size.

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