P/E ratio explained

Trailing vs forward P/E

Trailing P/E uses the last twelve months of reported earnings: factual but backward looking. Forward P/E uses analyst estimates for the coming year: relevant but only as good as the forecast.

A large gap between the two usually means earnings are expected to move sharply. Find out why before treating the lower number as the real one.

What counts as high or low

P/E is meaningful only against a peer group. Utilities and banks trade at structurally low multiples; software and consumer brands at high ones. Comparing a bank's P/E to a SaaS company's tells you nothing.

Compare a company to its own five-year range and to its closest listed competitors. That is where the ratio earns its keep.

When P/E breaks

Loss-making companies have no meaningful P/E. Cyclical businesses look cheapest at the top of the cycle, when peak earnings deflate the denominator, and expensive at the bottom.

One-off gains — an asset sale, a tax writeback — can halve a P/E for a year. Always check whether earnings came from operations.

Better used with other ratios

Pair P/E with return on equity and debt levels. A low P/E with high ROE and low debt is interesting; a low P/E with falling ROE and rising debt is a value trap.

The PEG ratio divides P/E by the earnings growth rate, giving a rough sense of whether a high multiple is justified.

Frequently asked questions

What is a good P/E ratio?

There is no universal number. Judge it against the company's own history and its sector peers.

Is a low P/E always better?

No. Low multiples often reflect declining earnings, high debt or governance concerns — the classic value trap.

How do I calculate P/E?

Divide the current share price by earnings per share over the last twelve months.