After finding the price of a particular stock, usually the next number everyone looks at is the P/E ratio.

P/E is the ratio of a company's share price to its per-share earnings.

A P/E ratio of 10 means that the company has 1 of annual, per-share earnings for every 10 in share price. (Earnings by definition are after all taxes etc.)

A company's P/E ratio is computed by dividing the current market price of one share of a company's stock by that company's per-share earnings. A company's per-share earnings are simply the company's after-tax profit divided by number of outstanding shares. A company that earned 5M last year, with a million shares outstanding, had earnings per share of 5. If that company's stock currently sells for 50/share, it has a P/E of 10. At this price, investors are willing to pay 10 for every 1 of last year's earnings.

P/Es are traditionally computed with trailing earnings (earnings from the past 12 months, called a trailing P/E) but are sometimes computed with leading earnings (earnings projected for the upcoming 12-month period, called a leading P/E).

For the most part, a high P/E means high projected earnings in the future. But actually the P/E ratio doesn't tell a whole lot, but it's useful to compare the P/E ratios of other companies in the same industry, or to the market in general, or against the company's own historical P/E ratios.

Some analysts will exclude one-time gains or losses from a quarterly earnings report when computing this figure, others will include it. Adding to the confusion is the possibility of a late earnings report from a company; computation of a trailing P/E based on incomplete data is rather tricky. (It's misleading, but that doesn't stop the brokerage houses from reporting something.) Even worse, some methods use so-called negative earnings (i.e., losses) to compute a negative P/E, while other methods define the P/E of a loss-making company to be zero. Worst of all, it's usually next to impossible to discover the method used to generate a particular P/E figure, chart, or report.

Like other indicators, P/E is best viewed over time, looking for a trend. A company with a steadily increasing P/E is being viewed by the investors as becoming more speculative. And of course a company's P/E ratio changes every day as the stock price fluctuates.

The P/E ratio is commonly used as a tool for determining the value of a stock. A lot can be said about this little number, but in short, companies expected to grow and have higher earnings in the future should have a higher P/E than companies in decline.

For example, if a company has a lot of products in the pipeline, I wouldn't mind paying a large multiple of its current earnings to buy the stock. It will have a large P/E. I am expecting it to grow quickly. A rule of thumb is that a company's P/E ratio should be approximately equal to that company's growth rate.

PE is a much better comparison of the value of a stock than the price. A 10 stock with a PE of 40 is much more "expensive" than a 100 stock with a PE of 6. You are paying more for the 10 stock's future earnings stream. The 10 stock is probably a small company with an exciting product with few competitors. The 100 stock is probably pretty staid - maybe a buggy whip manufacturer.

It's difficult to say whether a particular P/E is high or low, but there are a number of factors you should consider!

First: It's useful to look at the forward and historical earnings growth rate. (If a company has been growing at 10% per year over the past five years but has a P/E ratio of 75, then conventional wisdom would say that the shares are expensive.)

Second: It's important to consider the P/E ratio for the industry sector. (Food products companies will probably have very different P/E ratios than high-tech ones.)

Finally: A stock could have a high trailing-year P/E ratio, but if the earnings rise, at the end of the year it will have a low P/E after the new earnings report is released.

Thus a stock with a low P/E ratio can accurately be said to be cheap only if the future-earnings P/E is low.

If the trailing P/E is low, investors may be running from the stock and driving its price down, which only makes the stock look cheap.

Ioannis - Evangelos C. Haramis was born in Greece in 1951 and he studied in Greece, USA and in Belgium. He has been active in the stock markets since 1972. Since 2002 he is New Business Development Managing Director at an Investment Bank and the publisher of http://www.greekshares.com/

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