Understanding the PEG Ratio in Fundamental Analysis

The price/earnings to growth (PEG) Ratio tells you more than P/E alone

pegs and gavel
••• What exactly is the PEG ratio and how can it help investors?. Peter Dazeley/Photographer's Choice/Getty Images

 Though less well-known than its fundamental cousins, the Price/Earnings to Growth or PEG ratio can give you a more informed view of a stock's potential once you know how to use and interpret its results correctly.

The Formula Components

The price/earnings (P/E) ratio is a key component of the PEG ratio. You can calculate the P/E by taking a stock's current share price and dividing it by its earnings per share (EPS).

This number allows you to compare the relative value of a stock against other stocks, as well as determine if the market has priced a stock higher or lower in relation to its earnings.

The other component, earnings growth, refers to the percent change from one period to the next in terms of the company's projected earnings results.

Price/Earnings to Growth (PEG) Ratio

The Price/Earnings to Growth Ratio allows you to determine a stock's value, like with the P/E ratio, while also taking into consideration the company's earnings growth. This forward-looking component allows the PEG ratio to give you a more complete picture of a stock's fundamentals than you would get with the P/E alone.

You can calculate the PEG ratio by taking P/E and dividing it by the projected growth in earnings:

PEG = Price to Earnings Ratio / Projected Earnings Growth

For example, a stock with a P/E of 20 and projected earnings growth next year of 10 percent would have a PEG ratio of 2 (the P/E of 20 divided by the projected earnings growth percentage of 10 = 2).


The lower the PEG ratio, the more a stock may be undervalued relative to its earnings projections. Conversely, the higher the number the more likely the market has overvalued the stock.

Interpreting the Results

Using the PEG ratio in conjunction with a stock's P/E can tell a very different story than using P/E alone.

A stock with a very high P/E might be viewed as overvalued and not a good choice. Calculating the PEG ratio on that same stock, assuming it has good growth estimates, can actually yield a lower number, indicating that the stock may still be a good buy.

The opposite holds true as well. If you have a stock with a very low P/E you might logically assume that it is undervalued. However, if the company does not have earnings growth projected to increase substantially, you may get a PEG ratio that is, in fact, high, indicating that you should pass on buying the stock.

The Bottom Line

The baseline number for an overvalued or undervalued PEG ratio varies from industry to industry, but stock theory says that, as a rule of thumb, a PEG of below one is optimal. When a PEG ratio equals one, this means the market's perceived value of the stock has equilibrium with its anticipated future earnings growth. If a stock had a P/E ratio of 15, and the company projected its earnings to grow at 15 percent, for example, this gives it a PEG of one.   

When the PEG exceeds one, this tells you that the market expects more growth than estimates predict, or that increased demand for a stock has caused it to be overvalued.

A ratio result of less than one says that either analysts have set their consensus estimates too low, or that the market has underestimated the stock's growth prospects and value.

As with any analysis, the quality of results changes depending on the input data.  For example, a PEG ratio may be less accurate if calculated with historical growth rates, as compared to the ratio if a company has projected higher or upward-trending future growth rates.  

More on Fundamental Analysis Calculations