A price-to-earnings ratio, or P/E, is a company's share price divided by its earnings per share. It tells you how many dollars you are paying for each dollar of a company's annual profit. A stock at $100 a share with $5 of earnings per share has a P/E of 20, meaning investors pay $20 for every $1 of yearly profit.

How to calculate a P/E ratio

The formula is simple: share price divided by earnings per share (EPS). You can reach the same number by dividing a company's total market value by its total annual profit. Either way, the ratio answers one question: how much is the market paying for this company's earnings.

What makes it useful is comparison. A P/E on its own is just a number. Set against the company's own history, against rivals in the same industry, or against the market as a whole, it starts to say something about how cheap or expensive a stock is relative to what it earns.

A worked example with real numbers

Take Visa. For fiscal 2026, ended September 30, the company reported net income of $12.32 a share on a GAAP basis, in its October 27 filing. With the shares trading around $408 in late October 2026, that works out to a P/E of roughly 33 ($408 divided by $12.32). In other words, investors were paying about $33 for each dollar of Visa's trailing annual profit.

Whether 33 is a lot depends entirely on the context, which is the point of the next few sections. On its own, the figure is neither good nor bad. For where the earnings number comes from, see how to read a company earnings report.

Trailing versus forward P/E

There are two common versions. A trailing P/E uses earnings a company has already reported, usually the last 12 months. A forward P/E uses analysts' estimates of earnings over the next 12 months.

When a company's profits are expected to grow, the forward P/E is lower than the trailing one, because the denominator, future earnings, is bigger. That gap is why a stock can look expensive on trailing earnings and reasonable on forward estimates, or the reverse. Forward figures carry a health warning: they are forecasts, and forecasts are often wrong.

What counts as a high or low P/E

There is no universal pass mark. The honest answer is that a P/E only means something in context.

As a benchmark, the S&P 500 traded at a trailing P/E of about 26.3 as of October 27, 2026, according to data compiled by multpl.com. That is well above its long-run mean of roughly 16 and median of about 15, so US stocks as a group were priced richly relative to their own history. Individual companies vary enormously around that. A fast-growing software firm might trade at 40 times earnings because investors expect its profits to grow quickly; a mature utility or bank might trade at 10 to 12 because growth is slow and steady.

Corporate Finance Institute puts the general pattern simply: higher P/E ratios are typical of growth stocks, where investors pay up for expected future earnings, while lower P/E ratios are common among value stocks in mature industries. Neither is automatically better.

Comparing like with like

The single most common mistake with a P/E is comparing across industries. A software company and a utility are not priced on the same scale, because one is expected to grow fast and the other to pay steady dividends. A P/E of 30 can be ordinary in one sector and expensive in another. The useful comparison is within an industry, or against a company's own past, or against a broad benchmark like the S&P 500. That is why professional investors rarely quote a P/E without a peer group next to it. The number is a relative measure wearing the costume of an absolute one.

Why a low P/E can be a trap

It is tempting to read a low P/E as a bargain and a high one as overpriced. Both can mislead.

A low P/E sometimes signals a company in trouble, where the market expects earnings to decline, so the low price reflects risk rather than value. Investors call that a value trap. A high P/E can be justified if a company really does grow into it, or it can mean the stock is priced for perfection.

Three things distort the ratio and are worth checking. One-off items, such as a legal settlement or an asset sale, can inflate or depress a single year's earnings. Share buybacks reduce the share count and lift EPS, which lowers the P/E without the underlying business changing. And cyclical companies, like miners or carmakers, can show a misleadingly low P/E at the top of their cycle, when earnings are peaking.

P/E is a question, not an answer

The ratio is the starting point of analysis, not the end of it. A sensible way to use it is to ask why a number is what it is: compare a company with others in the same industry, look at trailing against forward, and check whether earnings are clean or distorted by one-offs and buybacks. A related measure, the PEG ratio, divides the P/E by the expected growth rate to put fast and slow growers on a fairer footing.

And remember a P/E needs positive earnings to exist at all. A company losing money has no meaningful P/E, which is why unprofitable firms are judged on revenue or other measures instead. For how the market as a whole is tracked, see what a stock market index is.