P/E Ratio (Price-to-Earnings)
$$\text{P/E} = \frac{\text{Stock Price}}{\text{Earnings Per Share (EPS)}}$$
What is P/E Ratio (Price-to-Earnings)?
The P/E Ratio (Price-to-Earnings) is calculated by dividing a company's current stock price by its Earnings Per Share (EPS). It is the most widely cited equity valuation multiple because it directly answers the investor's most fundamental question: how much am I paying for each dollar of annual profit?
The trailing P/E uses the most recent 12 months of reported EPS (also called LTM — last twelve months). The forward P/E uses consensus analyst estimates for the next 12 months of expected EPS. Forward P/E is typically lower than trailing P/E for growing companies (because earnings are expected to rise) and is the more decision-relevant figure for forward-looking investors.
The inverse of the P/E — EPS divided by Price — is the earnings yield, expressed as a percentage. It makes P/E directly comparable to bond yields. A P/E of 20 implies a 5% earnings yield. If a 10-year government bond yields 4.5%, the equity risk premium is modest. If bonds yield 2%, the equity risk premium is more comfortable.
When to use P/E Ratio (Price-to-Earnings)
Use P/E as a first-pass relative valuation: compare a company's P/E to its own historical range, to sector peers, and to the broader market index. A company trading at a P/E of 35 when peers average 18 is either higher quality, higher growth — or overvalued. Use forward P/E for growth companies where trailing earnings understate future profit potential.
Worked examples
| Company | Stock Price | EPS (TTM) | Trailing P/E | Earnings Yield | Sector Avg P/E | Relative Premium |
|---|---|---|---|---|---|---|
| Growth Tech | $180 | $4.50 | 40x | 2.5% | 28x | +43% |
| Mature Retail | $45 | $4.50 | 10x | 10% | 12x | −17% |
| Utility | $60 | $4.00 | 15x | 6.7% | 16x | −6% |
| Pharma | $120 | $8.00 | 15x | 6.7% | 18x | −17% |
Common pitfalls
P/E is meaningless for companies with negative earnings and misleading during earnings distortions (one-off charges, litigation settlements). A very low P/E can signal value or a value trap — a business in terminal decline. A high P/E requires high future earnings growth to justify; if growth disappoints, multiple compression can cause significant stock price declines even if the business remains fundamentally sound.
Frequently asked questions
What is a fair P/E ratio?
There is no universal fair P/E. The Shiller CAPE (cyclically adjusted P/E, averaging 10 years of real earnings) has historically averaged around 16–17 for the S&P 500, though this has risen significantly since 2010. Growth companies with 20–30% earnings growth can warrant P/Es of 30–50 if the growth materialises. The relevant comparison is always the company's earnings growth rate relative to the P/E — the PEG ratio (P/E divided by growth rate) adjusts for this.
Can P/E be negative?
P/E is undefined — not negative — when EPS is negative because the company has negative earnings. Some systems display a negative P/E in this case, but it is not analytically meaningful. For loss-making companies, analysts typically use Price/Sales, EV/Revenue, or a DCF model instead.
What is the difference between P/E and EV/EBITDA?
P/E is an equity-level metric using share price and per-share earnings — affected by capital structure (leverage) and tax. EV/EBITDA is a firm-level metric using Enterprise Value (equity + debt − cash) and pre-tax, pre-depreciation earnings — making it capital-structure neutral. EV/EBITDA is preferred for comparing companies with different leverage or tax profiles and is the dominant metric in M&A. P/E is easier to understand and more widely reported in public equity markets.