What is the Rule of 72?
From FinancialPlanning
The Rule of 72 is a simple shortcut for estimating the time required for your money to double, given a certain growth rate. The shortcut, with an example, is...
Take the interest rate (8%)
Divide it into the number 72 (72/8)
The result is the number of years required for your money to double (9 years)
It isn't exact but works pretty well for reasonable interest/growth rates.
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External Links
Math fans will enjoy the Wikipedia discussion of the Rule of 72, and the somewhat less memorable rule of 69.3/r X 200/(200-r).
