PEG Ratio: Formula, Calculation & What Is a Good PEG Ratio

The Price/Earnings-to-Growth ratio (PEG) adjusts the traditional P/E multiple for a company's expected earnings growth rate. It answers a question P/E alone cannot: is this stock expensive or cheap relative to how fast it's growing? A stock trading at 30x earnings might look expensive, but if earnings are expected to grow 30% annually, the PEG of 1.0 suggests the valuation perfectly aligns with growth. The same 30x P/E with only 10% expected growth yields a PEG of 3.0 — three times more expensive per unit of growth.

The PEG ratio was popularized by Peter Lynch, who managed the Fidelity Magellan Fund from 1977 to 1990, averaging 29% annual returns. Lynch used PEG as his primary screening tool and wrote extensively about it in One Up on Wall Street. His rule: a PEG below 1.0 suggests undervaluation, around 1.0 is fair, and above 2.0 is expensive. The elegance of PEG is that it bridges the value vs. growth divide — it allows fair comparison between a slow-growth value stock and a high-growth company by normalizing for the growth each offers. See how PEG fits into the Lynch GARP preset.

P/E Ratio is the current share price divided by trailing twelve-month earnings per share. Expected EPS Growth Rate is the analyst consensus estimate for annual earnings growth over the next 1–3 years, expressed as a whole number (20% growth = 20, not 0.20). Dividing P/E by the growth rate normalizes valuation for growth speed.

Example: a company with a P/E of 25 and 25% expected growth has a PEG of 1.0. The same P/E with 12.5% growth gives a PEG of 2.0. The PEG ratio is undefined when EPS growth is zero (division by zero) and produces hard-to-interpret results when growth or P/E is negative. This means PEG works best for profitable, growing companies — exactly where valuation discipline matters most.

Here's a step-by-step PEG ratio calculation using real-world logic:

Step 1: Find the P/E ratio. If a stock trades at $150 per share and earned $6 in EPS over the trailing twelve months, the P/E = $150 ÷ $6 = 25.0x.

Step 2: Find the expected EPS growth rate. Check analyst consensus estimates — suppose analysts project 20% annual EPS growth for the next two years.

Step 3: Divide: PEG = 25.0 ÷ 20 = 1.25.

A PEG of 1.25 means you're paying $1.25 of P/E for every percentage point of expected growth — moderately priced by Lynch's standards. Compare this to a slower-growing company: P/E of 12 with 5% expected growth gives PEG = 2.4, which is actually more expensive per unit of growth despite the lower headline P/E. This is the key insight: PEG reveals that a "cheap" low-P/E stock can be more expensive than a "pricey" high-P/E stock when you account for growth expectations. The UQS Valuation pillar scores PEG ≤ 0.5 as highly attractive and ≥ 3.0 as expensive.

Peter Lynch's framework: PEG below 1.0 = undervalued, around 1.0 = fairly valued, above 2.0 = expensive. In practice, PEG ratios below 1.0 are rare for high-quality companies because the market generally prices in expected growth. A PEG between 1.0 and 1.5 is considered attractive for quality growth stocks. Between 1.5 and 2.5 is typical. Above 3.0 means investors are paying a premium that requires continued growth acceleration to justify.

Context matters. A tech company with 30% growth at PEG 1.5 may be more attractive than an industrial with 5% growth at PEG 1.0, because the tech company's growth is likely to compound for more years. PEG also doesn't capture growth sustainability — a company expected to grow 40% for one year is valued the same as one expected to grow 40% for five years. That's why UQS pairs PEG with three other valuation metrics (earnings yield, P/FCF, and EV/EBITDA) — together they provide a more complete picture than any single ratio.

Low-PEG stocks are the core of Growth at a Reasonable Price (GARP) investing. These are companies growing faster than their P/E multiple suggests — the market is either underestimating their growth trajectory or temporarily discounting their sector. Historically, portfolios of low-PEG stocks have outperformed both pure value and pure growth strategies because they combine the upside of growth with the downside protection of reasonable valuation.

The Peter Lynch GARP preset in UQS weights Growth at 30% and Valuation at 25%, naturally surfacing stocks with favorable PEG ratios. The best growth stocks ranking is another starting point — sort by the ones with high growth scores AND high valuation scores, and you'll find stocks where the market hasn't fully priced in the growth. These low-PEG opportunities tend to cluster in sectors going through structural expansion (like AI infrastructure or energy transition) where consensus estimates lag reality.

A negative PEG ratio occurs when either the P/E ratio or the expected growth rate is negative — but not both. The most common scenario: a company has positive earnings (positive P/E) but analysts expect earnings to shrink (negative growth). Dividing a positive P/E by a negative growth rate produces a negative PEG. Less commonly, a company has negative earnings (negative P/E) with positive expected growth.

In either case, the negative PEG is essentially meaningless as a valuation metric — the Lynch framework of "below 1.0 = cheap, above 2.0 = expensive" doesn't apply. A negative PEG doesn't mean the stock is undervalued; it means the mathematical relationship between price and growth has broken down. The UQS scoring engine handles this by setting PEG to null when the result is negative or undefined, and redistributing the 25% weight to the remaining three Valuation metrics. This prevents a broken PEG calculation from distorting the overall valuation score.

The PEG ratio carries 25% weight in the Valuation pillar, scored on absolute thresholds: PEG ≤ 0.5 earns the highest score (100), PEG ≥ 3.0 earns the lowest (0), with linear interpolation between. Lower PEG scores better because it means you're paying less per unit of expected growth.

PEG creates a natural bridge between the Growth and Valuation pillars. A company with strong forward EPS growth (boosting the Growth score) automatically benefits from a lower PEG (boosting the Valuation score), creating coherent signals that GARP companies score well across both dimensions. When PEG is null — due to negative, zero, or unavailable growth estimates — the 25% weight redistributes to the remaining three Valuation metrics (earnings yield, P/FCF, EV/EBITDA). Read the full UQS methodology →