By Maksym Lytvynov, Founder of AlphaStocks | Last updated: 2026-09-23
Lynch PEG Ratio: How to Find Growth at a Reasonable Price
Peter Lynch managed the Fidelity Magellan Fund from 1977 to 1990. His central insight was disarmingly simple: a stock's P/E ratio should be compared to its earnings growth rate, not judged in isolation. The PEG ratio — Price/Earnings to Growth — formalized this idea and remains one of the most practical tools for identifying undervalued growth stocks.
What Is the PEG Ratio?
The PEG ratio normalizes a stock's P/E multiple by its expected earnings growth rate. It answers the question: how much am I paying per unit of growth?
PEG = P/E Ratio / Annual EPS Growth Rate (%)Example: A stock trades at a P/E of 25 and its earnings per share have grown 25% a year: PEG = 25 / 25 = 1. With only half that growth the PEG doubles, suggesting you are overpaying for the growth.
Why Dividend-Adjusted PEG Is More Accurate
The classic PEG formula penalizes companies that return earnings as dividends rather than reinvesting for growth. A utility at a P/E of 16 with 3% EPS growth and a 4% dividend has a plain PEG of 5.3, although its owners receive growth plus yield.
The dividend-adjusted PEG corrects this by adding the dividend yield to the growth rate in the denominator:
Dividend-Adjusted PEG = P/E / (EPS Growth Rate + Dividend Yield)Using the utility example: 16 / (3 + 4) = 2.29. Still not cheap, but a far more honest representation. AlphaStocks scores this one ratio, PEGY, for growers — for a company that pays no dividend it is simply the PEG. Its bands, from Lynch's own words: P/E (trailing twelve months, earnings from continuing operations) ÷ (5-year EPS growth % + dividend yield %) < 1; score 10 at PEGY ≤ 0.5, 8 at ≤ 0.67, 6 at ≤ 1, 3 at ≤ 2, else 0.
How Did Peter Lynch Categorize Stocks?
In One Up on Wall Street (1989), Lynch classified stocks into categories based on their growth characteristics. Each category calls for different expectations and different PEG thresholds:
| Category | How AlphaStocks assigns it (checked in this order) |
|---|---|
| Cyclical | GICS sector materials or energy, or a sub-industry naming steel, automobile, automotive parts, tires, airline, chemical, semiconductor, aluminum, paper, metals & mining; or net income falling to 50% or less of an earlier peak inside the 5-year window while revenue falls too |
| Turnaround | a loss in the latest fiscal year or any of the 3 before it |
| Asset Play | price below net assets per share (net current asset value or tangible book) |
| Slow Grower | 5-year EPS growth below 5% |
| Stalwart | growth from 5% to below 20% |
| Fast Grower | growth 20% or more |
Only slow growers, stalwarts and fast growers are scored on PEGY. A cyclical gets no P/E-to-growth score: its P/E looks lowest at the top of the cycle, just before earnings fall — the trap Lynch warned about. Turnarounds are judged on whether cash covers debt, asset plays on the discount of the price to net assets. The model does not rate banks and insurers.
Why Does a PEG Below 1.0 Signal Undervaluation?
A PEG of 1.0 means the market is pricing the stock at exactly one times its growth rate. Lynch considered this fair value. A PEG below 1.0 means the market is pricing the stock at a discount to its growth — you are paying less per unit of earnings growth than the market average.
Consider Alphabet (GOOGL): as an illustration, a P/E of 22 with EPS growth of 28% a year gives a PEG of 0.79. By Lynch's framework, that suggests the market is not fully pricing in the growth.
However, PEG has a critical dependency: whether the growth continues. AlphaStocks uses historical growth — the five-year EPS growth rate ending at the latest fiscal year, from SEC filings — not analyst forecasts, and a tiny base year gives no growth rate at all. If growth slows, the “bargain” PEG evaporates. This is why PEG is one input among several in the Value axis, not a standalone signal.
How AlphaStocks Uses the Lynch PEG Model
In the AlphaStocks composite scoring system, the Lynch model carries 25% of the Value axis in the general profile. The Value axis carries 10% of the composite and also sets the Timing axis (15%), the lower of Value and Momentum.
It sits alongside Graham fair value (45% of Value) and Greenblatt Magic Formula (30%of Value). Only the models that apply to a company are averaged. The three models approach valuation from different angles — asset-based, growth-adjusted, and earnings-yield-based — so that no single methodology drives the Value score.
Value = Graham × 0.45 + Greenblatt × 0.3 + Lynch × 0.25 (general profile)Limitations
PEG ratios are only as reliable as the growth rate in the denominator, and past growth does not guarantee future growth. That is why the model does not compute a PEG score for cyclicals or turnarounds at all.
The ratio also fails when earnings are negative or near zero, producing infinite or nonsensical values. When trailing EPS is not positive there is no P/E, and the PEGY test fails rather than reading as cheap; shrinking earnings score zero.
Finally, PEG does not account for balance sheet risk. The Lynch model adds his own balance-sheet checks — debt ÷ equity ≤ 25/75 (0.33); at 80/20 (4) or above, or with negative equity, the balance sheet is weak and caps the status at Neutral— and the composite scoring system addresses this by incorporating quality and timing dimensions that capture financial health and risk signals independently of valuation.
Frequently Asked Questions
What is the PEG ratio formula?
PEG = P/E Ratio / Annual EPS Growth Rate. For example, a stock with a P/E of 20 and an EPS growth rate of 20% has a PEG of 1.0. A PEG below 1.0 suggests the stock may be undervalued relative to its growth rate.
What is a good PEG ratio?
Lynch wrote that a fairly priced company has a P/E equal to its growth rate, so a PEG of 1 is fair and lower is better. For dividend payers he added the yield to growth and looked for (growth + yield) divided by P/E of 2 or better. AlphaStocks scores that as PEGY: P/E (trailing twelve months, earnings from continuing operations) ÷ (5-year EPS growth % + dividend yield %) < 1; score 10 at PEGY ≤ 0.5, 8 at ≤ 0.67, 6 at ≤ 1, 3 at ≤ 2, else 0.
How does AlphaStocks use the PEG ratio?
The Lynch model first puts each stock in one of Lynch's six categories, then values it the way its category is valued. Growers are scored on the dividend-adjusted PEG (PEGY), with growth taken as the five-year EPS growth rate ending at the latest fiscal year and the P/E on trailing-twelve-month earnings; cyclicals get no PEG score at all. It carries 25% of the Value axis in the general profile, and the Value axis carries 10% of the composite.
What are Peter Lynch's stock categories?
One Up on Wall Street names six: slow growers, stalwarts, fast growers, cyclicals, turnarounds and asset plays. AlphaStocks assigns them by rule, in this order: Cyclical — GICS sector materials or energy, or a sub-industry naming steel, automobile, automotive parts, tires, airline, chemical, semiconductor, aluminum, paper, metals & mining; or net income falling to 50% or less of an earlier peak inside the 5-year window while revenue falls too; Turnaround — a loss in the latest fiscal year or any of the 3 before it; Asset Play — price below net assets per share (net current asset value or tangible book); Slow Grower — 5-year EPS growth below 5%; Stalwart — growth from 5% to below 20%; Fast Grower — growth 20% or more.
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This article is for educational purposes only. AlphaStocks provides algorithm-generated research tools, not personalized investment advice. The PEG ratio is one component of a multi-factor scoring system. Growth rate estimates are based on analyst consensus and historical trends, not predictions by AlphaStocks. Past performance does not guarantee future results. Always conduct your own due diligence and consult a qualified financial adviser before making investment decisions. Data sourced from SEC EDGAR filings.