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\iteman{ZMATH 2000f.04345}
\itemau{Smith, Will}
\itemti{The 72 rule and other approximate rules of compound interest.}
\itemso{Parabola 36, No. 1, 7-15 (2000).}
\itemab
There is a simple approximate rule of thumb used by investors and accountants to estimate the time taken in years, $n$, for an investment to double with an interest rate of $R\%$, or indeed for a debt to double if left unpaid. One simply divides 72 by $R$ to estimate the time in years. The rule is known as ``Rule 72'' or ``the 72 Rule'' and is often attributed to the investment advisor Henri Aram who popularized it. This rule and a more accurate approximation are derived and discussed.
\itemrv{~}
\itemcc{F80}
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\itemli{}
\end