PEG Ratio (Price/Earnings-to-Growth)

Quick Definition

The PEG ratio (Price/Earnings-to-Growth ratio) divides a stock's P/E ratio by its expected earnings growth rate, adjusting valuation for growth. It addresses the P/E ratio's main weakness — that high P/E stocks might still be cheap if earnings are growing rapidly.

PEG Ratio = P/E Ratio / Expected Annual EPS Growth Rate

A PEG of 1.0 is traditionally considered fairly valued, below 1.0 potentially undervalued, and above 2.0 potentially expensive relative to growth.

What It Means

The P/E ratio has a critical flaw: it treats a 30x P/E on a company growing earnings at 5% the same as a 30x P/E on a company growing earnings at 40%. These situations are radically different — one is expensive, one may be cheap.

The PEG ratio solves this by incorporating growth. Peter Lynch, the legendary Fidelity Magellan Fund manager who averaged 29% annual returns from 1977-1990, popularized the PEG ratio and used it extensively. Lynch's rule: a fairly valued stock has a PEG of 1.0 (P/E equals growth rate). Under 1.0 is attractive; over 1.0 warrants scrutiny.

PEG Ratio Calculation Examples

The Peter Lynch Rule

Lynch's original framing: "A company growing earnings at 25% deserves a P/E of 25. One growing at 12% deserves a P/E of 12."

This is a rough rule of thumb, not a precise law, but it captures the core logic: the price you should pay for earnings is proportional to how fast those earnings are growing.

Lynch's PEG framework:

PEG Ratio Limitations

PEG vs. P/E: Practical Comparison

S&P 500 Historical Example:

The PEG ratio confirmed what many value investors sensed in 2021 — exceptional P/E multiples combined with modest expected growth produced PEG ratios signaling elevated valuation risk.

Forward vs. Trailing PEG

Most screeners default to forward PEG using consensus 5-year EPS growth estimates. Always verify which is being used before drawing conclusions.

Key Points to Remember

• PEG = P/E ratio divided by earnings growth rate — adjusts valuation for growth
• PEG below 1.0 suggests the growth rate is not fully priced in; above 2.0 suggests expensive relative to growth
• Peter Lynch popularized the rule: P/E should roughly equal EPS growth rate for fair value (PEG ≈ 1.0)
• The PEG ratio is only as good as the growth estimate used — garbage in, garbage out
• Not applicable to negative earnings, zero-growth, or deeply cyclical companies
• Use alongside other metrics — the PEG is a screening tool, not a definitive valuation verdict

Frequently Asked Questions

Q: What growth rate should I use for the PEG ratio? A: Most analysts use consensus forward 1-year or 3-5 year EPS growth estimates. Peter Lynch used the long-term expected growth rate. For consistency, use the same period when comparing companies. Always check what period the growth rate covers before using a published PEG figure.

Q: Why doesn't the PEG ratio work for value stocks or mature companies? A: Companies growing earnings at 3-5% would have very low PEG ratios (a 10x P/E on 3% growth = PEG 3.3) but should not necessarily trade at a P/E of 3x. Slow, reliable growth from a dominant business with strong dividends has value beyond what the PEG captures. PEG works best for growth companies with growth rates of 10%+.

Q: What's a good PEG ratio for tech stocks? A: Technology investors often accept higher PEG ratios (up to 2-3x) for companies with very durable competitive advantages, strong network effects, or market leadership in rapidly expanding end markets. The quality and durability of growth matters as much as the growth rate itself.