Lessons · Stocks · Beginner
The P/E ratio, simply
Price-to-earnings compares what you pay for a share with the earnings attached to that share - a starting point, not a verdict.
8 min read
What you will learn
- Compute and interpret a basic P/E
- Contrast trailing vs forward earnings
- Avoid common multiple traps
Key terms
- Trailing P/E
- Price divided by the last twelve months of reported earnings.
- Forward P/E
- Price divided by expected future earnings - depends on estimates.
- Earnings yield
- Roughly the inverse of P/E - earnings per unit of price.
1. The core idea
If a stock is $100 and earnings per share are $5, the trailing P/E is 20. You are paying $20 for each $1 of recent annual earnings - before growth, quality, and risk adjustments.
2. Context required
High P/E can mean high growth priced in - or depressed current earnings. Low P/E can mean value - or a value trap if profits are about to fall.
- Compare to sector peers and the company’s own history.
- Cyclicals often look “cheap” at peaks and “expensive” at troughs.
- One-time items can distort EPS; quality of earnings matters.
3. Beyond a single multiple
Serious work pairs multiples with growth, margins, balance sheet, and competitive position. P/E is a conversation starter.
Forward estimate risk
A stock at $50 with $2 trailing EPS has trailing P/E 25. If analysts expect $2.50 next year, forward P/E is 20 - but only if that $2.50 arrives. Missed estimates rewrite the multiple overnight.
Common mistakes
- Buying low P/E without checking earnings quality
- Treating forward P/E as a fact instead of a forecast
- Comparing P/Es across very different industries blindly
Try this on StockWatch
- Open fundamentals on a quote page when available
- Compare peer names with Compare
- Read earnings-related Upcoming items for the symbol