P/E ratio of a stock: what it means, how it is calculated and when a low P/E is a trap

What P/E is

P/E (price/earnings) is the share price divided by earnings per share (EPS). It tells you how many euros the market pays for one euro of annual profit. A P/E of 10 means that, with profit unchanged, the investment would "pay back" its price through 10 years of earnings — it is a measure of expectations, not a guarantee.

A low P/E is not automatically "cheap"

A low P/E can mean a low price, but also a market expectation of falling profit, a one-off (non-repeatable) profit in the denominator, or structurally lower growth. A high P/E can reflect expected growth — or overvaluation. The number alone does not distinguish the two cases; context (the profit trend, the sector, the quality of earnings) does.

It is not compared across sectors

Banks, insurers and holding companies have a different earnings structure from industrial companies, so P/E is meaningfully compared within a sector, not between sectors. For financial companies, capital metrics (P/B together with ROE) often say more than P/E; for holdings, the sum of the parts (SOTP).

What to watch in the denominator

• One-off items: an asset sale or a write-off inflates/crushes a single year's EPS — a P/E on that base is misleading.
• Minority interests: for groups, what matters is the profit attributable to the parent, not the total consolidated figure.
• Share count: treasury shares and new issues change EPS without any change in the business.

P/E is useful as a quick comparative measure within a sector and over time for the same company — with a check of what sits in the denominator. No single ratio is enough for a decision.

*Educational content — not investment advice or a recommendation to buy or sell any security.*