The Longer the Payback Period, the Greater the Risk

The most useful thing about payback periods is that they give a good (albeit rough) idea of how risky an investment is. 

We may feel fairly confident in our assessment of a company's earnings potential over the next year or so, but that confidence usually diminishes as we peer farther into the future. 

Thus, the longer the payback period, the greater risk we run that we won't get the return we expect. 

That is especially true if the company we're looking at is a young firm without an established market position or is dependent on a rapidly changing technology.

Take Qualcomm QCOM, for example. This digital-wireless-communications powerhouse was the hottest stock on Wall Street in 1999 after appreciating 12-fold in 11 months. Its PEG payback is 12.4 years--not too bad considering its $350-plus stock price. But compare that with Allstate ALL, which watched its stock drop about 30% in 1999. Its PEG payback is 6.6 years. 

Qualcomm may be the sexier company and certainly has had upside for its investors, but sometimes the cheaper stock looks like a better deal.

After all, stocks with longer payback periods aren't just riskier, they also have lower rewards. 

Remember that the payback period is the amount of time it takes to double your money. 

If a stock has a payback period of five years, that means it doubles the amount of the original investment in five years. An investment that doubles in five years has an average rate of return of 15% per annum (on a scientific calculator, take the fifth root of 2, subtract 1, and multiply by 100). 

A payback period of 10 years implies a rate of return of a little more than 7%. At 20 years, the rate is less than 4%. And so on. 

The longer the payback period, the lower the rate of return.