PEG Ratio

The PEG ratio adjusts P/E for expected earnings growth. Peter Lynch popularized it as a way to compare stocks across different growth rates on a level playing field.

The intuition is simple: a stock trading at P/E 30 with 30% growth (PEG = 1.0) may be as fairly valued as one at P/E 10 with 10% growth (PEG = 1.0). Lynch considered PEG below 1.0 as potentially undervalued.

PEG has important limitations. It assumes a linear relationship between P/E and growth that does not hold at extremes. It also inherits all the weaknesses of forward earnings estimates, including systematic analyst optimism. Empirical factor research has found PEG to be a weak standalone predictor of returns.

PEG below 1.0 suggests the stock may be undervalued relative to its growth rate. PEG above 2.0 suggests the market is paying a high premium over the growth rate.

PEG works best as a comparative tool within a sector - ranking similar companies by PEG can highlight which ones offer the most growth per unit of valuation.

Value investors should be cautious with PEG. It blends a backward-looking metric (trailing P/E) with a forward-looking one (estimated growth), creating a false precision. Companies with stable, predictable growth produce more reliable PEG ratios than cyclicals or turnarounds.

Growth sectors (technology, biotech) often show PEG ratios below 1.0 for companies with very high expected growth, but this can be misleading if growth estimates prove optimistic.

Mature sectors (utilities, consumer staples) tend to show PEG ratios above 1.5 because growth rates are low (3-8%) while P/E ratios remain moderate. A utility with PEG of 2.0 is not necessarily overpriced - it reflects the market pricing stability and dividends.

PEG is least useful for cyclical sectors where growth rates swing wildly and estimates are unreliable.