What Is the P/E Ratio? How to Use Price-to-Earnings

The price-to-earnings (P/E) ratio tells you how much investors are paying for each dollar of a company's profit. It's the most widely quoted valuation measure and a common starting point for judging whether a stock looks cheap or expensive.

How to calculate P/E

P/E = share price ÷ earnings per share (EPS)

If a stock trades at $100 and earned $5 per share over the last twelve months, its P/E is 20. In other words, investors are paying $20 for every $1 of annual profit.

Trailing vs. forward P/E

• Trailing P/E uses actual earnings from the last 12 months. It's based on real results but looks backward.
• Forward P/E uses analysts' estimates of the next 12 months' earnings. It looks ahead but depends on forecasts that may be wrong.

For a fast-growing company, forward P/E is usually much lower than trailing P/E, because earnings are expected to rise.

What a high or low P/E means

A high P/E usually means investors expect strong future growth, or that the stock is simply expensive. A low P/E can signal a bargain, slow expected growth, or problems the market is worried about. The P/E alone can't tell you which, so context matters.

What's a "good" P/E?

There's no single good number. Over long periods, the S&P 500's average P/E has been in the mid-to-high teens, but it has ranged widely, and different industries trade at very different levels. Fast-growing software companies often carry far higher P/Es than banks, utilities or energy companies. The most useful comparisons are:

• Against close competitors in the same industry.
• Against the company's own history: is it cheaper or more expensive than its usual range?
• Against its growth rate, using the PEG ratio.

Earnings yield: P/E flipped

Dividing earnings by price (the inverse of P/E) gives the earnings yield. A P/E of 20 equals a 5% earnings yield. This makes it easy to compare a stock with bond yields or with free cash flow yield.

Limitations of the P/E ratio

• No earnings, no P/E: companies with losses have no meaningful P/E.
• One-time items: gains or charges can distort a single year's earnings.
• Ignores debt and cash: two companies with the same P/E can have very different balance sheets. EV/EBITDA accounts for this.
• Cyclical traps: for cyclical businesses, the P/E often looks lowest at the peak of the cycle, when earnings are about to fall, and highest at the bottom.
• Accounting choices affect earnings more than cash. Check cash flow too.

Using P/E in your research

Treat the P/E as one input alongside growth, profitability and the balance sheet, not a buy or sell signal on its own. Every StockEngine stock page shows the trailing P/E with other valuation metrics, the stock screener lets you filter by P/E range, and the compare tool lines up P/Es side by side. For a fuller valuation, estimate intrinsic value with the DCF calculator and read intrinsic value and DCF.

This article is educational and not investment advice.

Frequently asked questions

What is a good P/E ratio?

There isn't one number that's good for every stock. P/E ratios vary widely by industry and growth rate, so compare a company with close competitors and with its own history, and consider the PEG ratio to adjust for growth.

Is a low P/E ratio always better?

No. A low P/E can signal a bargain, but it can also reflect slow growth, cyclical peak earnings or problems investors expect ahead.

What does a negative P/E mean?

It means the company lost money over the period, so the P/E isn't meaningful. Investors usually look at measures such as price-to-sales or future earnings estimates instead.