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Rule 72 says divide 72 by the interest rate (percent) and this is approximately the number of years it will take to double your money.

72/10 = 7.2 -> 10% will give you double $ in 7.2 years

72/6 = 12 -> 6% will give you double $ in 12 years

The exact time to double is found by a much more complex equation involving logarithms. Rule 72 gives very close to the exact answer.

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