Price-to-Earnings (P/E) Ratio Formula
The P/E ratio formula measures how much investors pay per dollar of earnings.
Learn trailing vs. forward P/E with examples.
The Formula
The Price-to-Earnings (P/E) ratio tells you how much investors are willing to pay for every $1 of a company's earnings. A P/E of 20 means investors pay $20 for each $1 of annual profit.
Variables
| Symbol | Meaning | Unit |
|---|---|---|
| P/E | Price-to-Earnings ratio | ratio (no unit) |
| Market Price Per Share | Current trading price of one share | $ |
| EPS | Earnings Per Share — net profit divided by shares outstanding | $ per share |
Trailing P/E vs. Forward P/E
Trailing P/E uses actual earnings from the past 12 months (TTM — trailing twelve months). It is based on real, reported data and is more reliable but looks backward.
Forward P/E uses analyst estimates of earnings for the next 12 months. It reflects expectations about future growth, but estimates can be wrong.
Example 1 — Basic P/E Calculation
A stock trades at $150 per share. Its EPS over the past 12 months was $7.50.
P/E = $150 / $7.50
P/E = 20 — investors pay $20 for every $1 of earnings.
Example 2 — Forward P/E
The same stock trades at $150. Analysts estimate next year's EPS at $10.00.
Forward P/E = $150 / $10.00
Forward P/E = 15 — a lower forward P/E suggests earnings are expected to grow.
Reference Values
- The S&P 500 historical average P/E is approximately 15–25.
- P/E below 15 may indicate an undervalued stock — or a struggling business.
- P/E above 30 often reflects high growth expectations or potential overvaluation.
- Growth stocks (like technology companies) typically have higher P/E ratios than value stocks.
- P/E is meaningless for companies with negative earnings — use other metrics in that case.
When to Use It
- Comparing valuation between two companies in the same industry
- Benchmarking a stock against the market average or its own historical P/E
- Quickly screening whether a stock appears expensive or cheap relative to earnings
- Understanding market sentiment — a high P/E suggests high growth expectations
Limitations
- P/E does not account for debt — use EV/EBITDA for a more complete picture.
- One-time charges can distort EPS and make P/E misleading.
- P/E should always be compared within the same industry — sectors have very different norms.