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Calculation
P/E Ratio = Stock Price ÷ Earnings Per Share
Example: Apple
- Stock price: $150
- Earnings per share (EPS): $6
- P/E ratio: $150 ÷ $6 = 25
Interpretation: You're paying $25 for every $1 of annual earnings.
Interpretation
Low P/E (<12): Suggests stock is cheap
- Either: Market is pessimistic, or company is in decline
- Example: 2009 after financial crisis, S&P 500 P/E was 13 (cheap)
Fair P/E (15-20): Market values company at average
- Typical for mature companies with steady growth
High P/E (>25): Suggests stock is expensive
- Either: Market is optimistic about growth, or valuation bubble
- Example: Tech stocks in 2000 peak, P/E of 40+
- Example: Tesla at P/E of 70-100 (reflects growth expectations)
Historical average P/E: 16-18
Trailing vs. Forward P/E
Trailing P/E:
- Based on past 12 months of earnings
- Backward-looking
- Useful for understanding what you paid
Forward P/E:
- Based on projected next 12 months of earnings
- Forward-looking
- More useful for valuation (reflects what you expect to earn)
Example: Company that grew earnings 20% last year and is expected to grow 20% again
Trailing P/E: 25 Forward P/E: 20 (higher projected earnings make it less expensive)
Forward P/E is more useful, but future earnings are uncertain.
P/E and Growth
P/E should be compared to growth rate:
PEG Ratio = P/E Ratio ÷ Growth Rate
Example 1:
- Stock A: P/E of 20, growth 5%
- PEG: 20 ÷ 5 = 4 (expensive relative to growth)
Example 2:
- Stock B: P/E of 40, growth 30%
- PEG: 40 ÷ 30 = 1.3 (cheap relative to growth)
A PEG ratio near 1.0 suggests fair valuation given growth expectations.
Industry Variation
P/E varies dramatically by industry:
Utilities: P/E 12-16 (stable, low-growth) Banks: P/E 10-14 (stable, cyclical) Consumer goods: P/E 18-22 (stable, consistent) Tech: P/E 25-40+ (higher growth expectations) Biotech/Pharma: P/E 15-25 (high growth, patent risk)
Comparing a utility (P/E 14) to a tech company (P/E 40) and concluding the utility is cheaper is wrong—they have different growth profiles.
Earnings Manipulation
P/E can be misleading if earnings are manipulated:
Stock buybacks: Company buys its own shares, reducing share count
- Earnings stay same; earnings per share rise
- P/E looks lower even if nothing improved
One-time gains: Selling assets creates one-time earnings
- Makes recurring earnings look artificially high
- P/E looks low on inflated earnings
Accounting practices: Different depreciation methods, inventory accounting can affect reported earnings
This is why P/E must be combined with other metrics.
P/E in Market Cycles
Late expansion (late bull market):
- P/E expands (rises)
- Stock prices rise even though earnings growth slows
- Example: 2000 tech bubble, S&P 500 P/E hit 44
Peak/early contraction (late bull → bear):
- P/E contracts (falls)
- Stock prices crash on declining earnings expectations
Trough/early expansion (bear → bull):
- P/E is very low (attractive)
- Stock prices start rising
- Example: 2009 bottom, S&P 500 P/E was 13
S&P 500 Historical P/E
1950: ~8 (cheap) 1973: ~8 (cheap) 1987: ~18 (fair) 2000: ~30-44 (expensive; peak of dot-com bubble) 2009: ~13 (cheap; bottom of financial crisis) 2020: ~18-20 (fair) 2024: ~25 (slightly expensive)
Currently, S&P 500 P/E is about 25, slightly above historical average, suggesting valuations are moderately expensive.
P/E and Returns
Historically, investing when P/E is low (cheap valuations) produces better returns:
Investing at P/E of 12-15: Expected 10-year return ~8-10% Investing at P/E of 20-25: Expected 10-year return ~6-7% Investing at P/E of 30+: Expected 10-year return ~3-5%
The higher the current P/E, the lower the expected future return. This is mean reversion.
Limitations of P/E
1. Doesn't account for quality: High-quality company with stable earnings deserves higher P/E than low-quality company
2. Doesn't account for debt: Company A: P/E of 20, no debt | Company B: P/E of 20, high debt | Company B is riskier
3. Doesn't account for growth: A company with 20% growth deserves higher P/E than 0% growth company
4. Cyclical biases: Cyclical companies (banks, auto manufacturers) have low earnings in recessions, making P/E look high
5. Momentum effects: Some high-P/E stocks continue rising (momentum) even though valuations seem expensive
Using P/E Effectively
1. Compare within industry: Utility P/E of 14 vs. tech P/E of 35 isn't directly comparable
2. Check forward P/E: More forward-looking than trailing
3. Combine with other metrics: P/E + P/B (price-to-book) + debt + growth rate
4. Understand the cycle: High P/E at bull market peak is riskier than high P/E at bull market start
5. Don't rely solely on P/E: Fundamental analysis requires multiple metrics
The Bottom Line
P/E ratio is a useful valuation metric but incomplete. A low P/E doesn't guarantee a good investment (could be declining), and a high P/E doesn't guarantee a bad investment (could be growing rapidly).
Use P/E as one component of valuation analysis, comparing to historical norms, industry averages, and growth expectations.
