The formula in one line
The price-to-earnings ratio (P/E) divides a stock's share price by its earnings per share (EPS): P/E = Share Price ÷ EPS. A P/E of 20 means investors are paying $20 for every $1 of annual earnings the company produces. The number is a valuation shortcut — a single ratio that captures the relationship between what the market charges for a share and what the underlying business earns per share.
Compute the ratio for any ticker — with EPS auto-filled from filings — using the P/E ratio calculator. For a refresher on EPS itself, see EPS explained.
Trailing vs forward — same shape, different inputs
Trailing P/E uses EPS from the past four quarters (TTM — trailing-twelve-months). It is backward-looking and uses real, reported numbers. Most financial sites publish trailing P/E by default.
Forward P/E uses analyst-consensus EPS for the next four quarters. It is forward-looking and depends on estimates that can be revised. Forward P/E is usually lower than trailing P/E for a growing company (because earnings are expected to rise) and higher than trailing for a declining company.
Quoting a single P/E number without specifying trailing or forward is ambiguous — always check which variant a source is using.
What counts as a "normal" P/E?
There is no universal "fair" P/E — the answer depends on the industry, the growth rate, and the prevailing interest-rate environment. As a rough order of magnitude:
- S&P 500 long-run average: roughly 15–20 trailing.
- Mature low-growth sectors (utilities, consumer staples, banks): typically 10–18.
- Cyclical industries at trough earnings: can show optically high P/E (30–60) because the denominator is depressed.
- High-growth tech / software: commonly 30–80, sometimes triple digits.
- Companies with negative earnings: P/E is undefined — the metric breaks down.
Why a high P/E is not automatically "overvalued"
P/E is a snapshot. A high ratio reflects market expectations of future earnings growth, not just current earnings. A company growing earnings at 30% per year can justify a P/E far above the market average — within a few years today's expensive P/E becomes tomorrow's cheap one.
Conversely, a low P/E is not automatically a bargain. Cyclical companies near peak earnings often look "cheap" right before earnings collapse. A low P/E in a structurally shrinking industry can stay low or get lower.
More useful comparisons: same company over time (P/E vs its own 5-year history), same sector (peer P/Es), or normalised against expected growth (PEG ratio). For cross-company size comparisons by absolute earnings, see the top companies by earnings ranking.
Related concepts and tools
- EPS explained — basic vs diluted, the denominator of P/E.
- Market capitalization explained — P/E times earnings equals market cap; the two ratios are linked.
- P/E ratio calculator — auto-fills price and EPS for any ticker.
- Price target methodology — how historical P/E feeds bear/base/bull projections.
To check the current P/E for a specific stock, open any company hub and use the P/E calculator with the ticker pre-selected.