P/E Ratio

Dollars paid per dollar of profit

Take the price of one share of a stock and divide it by the company's earnings per share over a year. A $60 share backed by $4 of earnings per share trades at a P/E of 15: investors are paying $15 for every $1 of current annual profit. The same number falls out at the company level too: divide the market capitalization by total annual profit and you get the identical ratio.

Flip it over and the P/E becomes an earnings yield: at a P/E of 15, the business earns about 6.7% of its price each year. That inversion is a handy way to compare a stock's profit engine against what other assets pay.

What a high or low P/E is saying

A high P/E means investors are paying a lot for today's profit, usually because they expect it to grow quickly. A low P/E means they are paying little, usually because they expect stagnation or decline. Each reading has a dark twin: the expensive stock may simply be overvalued, and the cheap one may be a genuine bargain the market has misjudged.

The honest way to use the ratio is as a question, not an answer. A P/E of 30 asks: what growth would justify paying 30 times profit, and do I believe this company will deliver it? A P/E of 8 asks: what is the market worried about, and is the worry overdone?

Trailing vs forward

A trailing P/E uses the last twelve months of reported earnings: real audited numbers, but backward-looking. A forward P/E uses analyst estimates of the coming year's earnings: closer to what you are actually buying, but only as reliable as the estimates. Quoted P/E figures often differ between sources simply because one is trailing and the other is forward, so check which you are reading before comparing anything.

Where the ratio breaks

No earnings, no P/E. A company losing money has a negative or absent ratio, which is common among young growth companies, and their disappearance from P/E screens says nothing about whether they are good or bad investments. The ratio simply cannot see them.

Cyclical earnings distort it. A miner or energy producer at the top of a commodity cycle posts huge profits, making its P/E look temptingly low at exactly the wrong moment; at the bottom of the cycle, collapsed earnings make the same company look absurdly expensive just when it may be cheapest. Steadier businesses, banks and utilities among them, have earnings that mean more when divided into a price.

Sector norms differ. Software companies routinely trade at higher multiples than banks or pipelines, for structural reasons: growth rates, capital intensity, regulation. Comparing a stock's P/E to a company in a different sector misleads more than it informs. Compare it to its own sector and to its own history.

Using it humbly, and together

The P/E of an entire market works as a rough temperature gauge. Far above its long-run range, optimism is expensive; far below, pessimism is on sale. It is a slow, imprecise signal that says nothing about the next year, and extremes can persist far longer than anyone expects, so it earns humility rather than market timing.

For individual stocks, the P/E only works in company: alongside growth prospects, debt levels and the durability of the business. On its own, it mostly measures how the market already feels. And for index fund and ETF investors, all of this is largely trivia: if you buy the whole market, you accept the market's average valuation, whatever it happens to be.