The '''Rule of 72''' is used to estimate [[Interest|compound interest]], specifically how long it takes money to double under a given interest rate. The number 72 is placed into the [[Numerator|numerator]] and the rate of interest in the [[Denominator|denominator]]. The quotient is the number of years needed for the money to double, up to a small [[Rounding_error|rounding error]].
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The '''Rule of 72''' is used to estimate [[Interest|compound interest]], specifically how long it takes money to double under a given interest rate. The number 72 is placed into the [[numerator]] and the rate of interest in the [[denominator]]. The quotient is the number of years needed for the money to double, up to a small [[rounding error]].