What PEG fixes about P/E
The P/E ratio alone is a blunt instrument: it tells you what the market pays for a dollar of earnings, but not why. A software company at 30x earnings might be cheap if it is compounding at 25%, while a utility at 15x might be expensive if it grows at 3%. PEG divides P/E by growth, so it puts both on the same scale. In that example the software company has a PEG of 1.2 and the utility a PEG of 5 — the expensive-looking stock is actually the better value per unit of growth. To see what growth the current price implies, pair PEG with our reverse DCF calculator.
Why it fails for slow growers, cyclicals and negative EPS
PEG needs a positive earnings base and a positive, sustainable growth rate. If EPS is negative, P/E is undefined and PEG is nonsense. If growth is near zero, even a modest P/E produces a huge PEG, which is mathematically true but practically useless — a stable utility should be judged on dividend yield and balance sheet, not growth-adjusted P/E. Cyclicals break it in a different way: a single year's growth rate is not representative of the cycle, so PEG can look extreme at the top and deceptively cheap at the bottom.
Context matters. A PEG of 1.5 means something different in software than in industrials. Cross-check against sector norms using our average P/E ratio by industry guide, and consider the industry benchmarks for related metrics like EV/EBITDA.
Reading the bands
The result labels PEG below 1.0 as "Low PEG — growth may be underpriced", 1.0–2.0 as "In typical range", and above 2.0 as "High PEG — paying up for growth". These are rules of thumb, not hard cut-offs. A PEG of 2.2 on a company with durable 20% growth and a wide moat can still work; a PEG of 0.8 on a business with deteriorating margins can be a value trap. Use the bands to rank ideas, then do the work on quality.
Worked example
A stock trades at $150 with EPS of $5.00, expected EPS growth of 15% and a 0.5% dividend yield. P/E = 30, PEG = 30 ÷ 15 = 2.00. That lands at the top of the typical band — the market is paying full price for the growth. If you include the dividend, PEGY = 30 ÷ 15.5 = 1.94, marginally more attractive. The sensitivity table shows PEG at growth rates from 10% to 20%: at 10% growth PEG is 3.0, at 20% it is 1.5. Your view on which growth rate is realistic is the real decision.