The price-to-earnings ratio compares a company’s share price to its earnings per share. It answers a simple question: how many dollars are investors willing to pay today for one dollar of the company’s annual profit? A P/E of 20 means the market is paying $20 for every $1 of earnings.
It is the most widely quoted valuation multiple because it is quick to compute and easy to compare across companies — though, as with any single number, it hides as much as it reveals.
Trailing P/E uses the last 12 months of actual EPS; forward P/E uses analysts’ estimate of next year’s EPS.
Suppose a stock trades at $150 and earned $6.00 per share over the last year:
Investors are paying 25× earnings. If a competitor with similar growth trades at a P/E of 15, the first company is more richly valued — the market expects more from it, or it is simply more expensive.
P/E is most useful relative to a reference point: the company’s own history, its direct peers, or its sector average. A P/E below the peer group can flag a potential bargain; well above it signals high expectations that the business must keep meeting.
Pair it with a growth measure. A high P/E is easier to justify when earnings are growing quickly — which is the logic behind the PEG ratio (P/E divided by growth rate).
P/E matters most for stable, consistently profitable companies, where earnings are a meaningful anchor. Comparing mature businesses in the same industry is where it earns its keep.
P/E breaks down when earnings are near zero, negative, or distorted by one-off items — the ratio becomes huge or meaningless. It ignores debt entirely (unlike EV/EBITDA), says nothing about cash generation, and can be inflated by accounting choices. A low P/E is sometimes a value trap: cheap for a good reason.