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What It Is:

The price-to-earnings ratio (P/E) is a valuation method used to compare a company’s current share price to its per-share earnings.

How It Works/Example:

The market value per share is the current trading price for one share in a company, a relatively straightforward definition. However, earnings per share (EPS) may not be as intuitive for most investors. The more traditional and widely used version of the EPS calculation comes from the previous four quarters of the price-to-earnings ratio, called a trailing P/E. Another variation of the EPS can be calculated using a forward P/E, estimating the earnings for the upcoming four quarters. Both sides have their advantages, with the trailing P/E approach using actual data and the forward P/E predicting possible outcomes for the stock. Calculated as the following;

Price-to-Earnings Ratio (P/E) = Market value per share / Earnings Per Share (EPS)

Moving on from the basics, let us do a sample calculation with company XYZ that currently trades at $100.00 and has an earnings per share (EPS) of $5.00. Using the previously mentioned formula, you can calculate that XYZ’s price-to-earnings ratio is 100 / 5 = 20.

For more explanation of how to use the P/E ratio in conjunction with other valuation ratios, please read our educational article Don't Be Misled By the P/E Ratio.

Why It Matters:

The price-to-earnings ratio is a powerful, but limited tool. For investors, it allows a very quick snapshot of the company’s finances without getting bogged down in the details of an accounting report.

Let us use our previous example of XYZ, and compare it to another company, ABC. Company XYZ has a P/E of 20, while company ABC has a P/E of 10. Company XYZ has the highest P/E ratio of the two and this would lead most investors to expect higher earnings in the future than from company ABC (which possesses a lower P/E ratio).

As noted earlier, the P/E ratio is limited. It does not paint the entire picture for the potential investor; rather it is a complementary tool in your financial toolbox. Be wary of forward EPS measures, (remember, EPS is an essential aspect of calculation of the P/E ratio) as they are matters of prediction and are only estimates of projected earnings. Further, trailing P/E ratios can only tell you what happened to a company in the previous time periods.