What Is P/E Ratio?
The P/E ratio measures a stock's price relative to its earnings per share. Learn how to calculate P/E, what's a good P/E ratio, and how investors use it.
Definition
The P/E ratio (price-to-earnings ratio) is a valuation metric that compares a company's current stock price to its earnings per share (EPS). The formula is simple: P/E = Stock Price / Earnings Per Share. If a stock trades at $100 and earned $5 per share over the past year, its P/E ratio is 20.
A P/E of 20 means investors are willing to pay $20 for every $1 of earnings. The higher the P/E, the more investors are paying for each dollar of profit -- typically because they expect strong future growth. Lower P/E stocks may be undervalued bargains or struggling companies. Context matters enormously.
There are two common versions: trailing P/E (using the last 12 months of actual earnings) and forward P/E (using analysts' estimates of next year's earnings). The S&P 500's historical average P/E is roughly 15-17. During bubbles, it has exceeded 30; during crashes, it has dipped below 10.
Real-World Example
Suppose Company A and Company B both trade at $100 per share. Company A earned $10 per share (P/E = 10), while Company B earned $2 per share (P/E = 50). Company A appears cheaper -- you get more earnings for your dollar. But Company B might have a P/E of 50 because the market expects its earnings to grow rapidly. Neither is automatically a better investment; the P/E just tells you how much you're paying relative to current earnings.
Why It Matters
P/E is the most widely used stock valuation metric in the world. It provides a quick gut-check on whether a stock is expensive or cheap relative to its earnings. Value investors like Warren Buffett look for stocks trading at reasonable P/E ratios relative to their growth rates. Growth investors may accept high P/E ratios if they believe earnings will grow fast enough to justify the premium. Either way, understanding P/E is essential for evaluating any individual stock.
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Frequently Asked Questions
What is a good P/E ratio?
There is no universal 'good' P/E. The S&P 500 average is about 15-17. Growth stocks may have P/E ratios of 30-50+, while value stocks might trade at 8-15. Compare a stock's P/E to its industry peers and historical average for the most useful context.
Can a P/E ratio be negative?
Yes. If a company is losing money (negative earnings), the P/E ratio is negative or not meaningful. Most financial databases show 'N/A' for companies with negative earnings.
What is the difference between trailing and forward P/E?
Trailing P/E uses the last 12 months of actual reported earnings. Forward P/E uses analysts' consensus estimate for the next 12 months of projected earnings. Forward P/E is more forward-looking but relies on estimates that may be wrong.
Should I only buy stocks with low P/E ratios?
Not necessarily. A low P/E can mean a stock is undervalued, but it can also mean the company has fundamental problems or declining earnings. Always consider why the P/E is low before buying.
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