When it comes to valuing stocks, the price/earnings ratio is one of the oldest and most frequently used metrics. Although a simple indicator to calculate, the P/E is actually quite difficult to interpret. It can be extremely informative in some situations, while at other times it is next to meaningless. As a result, investors often misuse this term and place more value in the P/E than is warranted.
The P/E Ratio: What is the P/E Ratio?
P/E is short for the ratio of a company's share price to its per-share earnings. As the name implies, to calculate the P/E you simply take the current stock price of a company and divide by its earnings per share (EPS):
P/E Ratio = Market Value per Share
Earnings per Share (EPS)
Most of the time, the P/E is calculated using EPS from the last four quarters. This is also known as the trailing P/E. However, occasionally the EPS figure comes from estimated earnings expected over the next four quarters. This is known as the leading or projected P/E. A third variation that is also sometimes seen uses the EPS of the past two quarters and estimates of the next two quarters.
There isn't a huge difference between these variations. But it is important to realize that, in the first calculation, you are using actual historical data. The other two calculations are based on analyst estimates that are not always perfect or precise.
Companies that aren't profitable, and consequently have a negative EPS, pose a challenge when it comes to calculating their P/E. Opinions vary on how to deal with this. Some say there is a negative P/E, others give a P/E of 0, while most just say the P/E doesn't exist.
Historically, the average P/E ratio in the market has been around 15-25. This fluctuates significantly depending on economic conditions at the time. The P/E can also vary widely between different companies and industries.
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