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PEG Ratio Explained: The Growth-Adjusted P/E

Learn how the PEG ratio adjusts P/E for growth, how to calculate it, what a good PEG ratio is, and when this metric works best for stock analysis.

Meet Dhanani
By Meet Dhanani

Senior Software Engineer at Red Hat

The PEG ratio solves the biggest limitation of the P/E ratio: it doesn’t account for growth. A company with a P/E of 40 might be cheap if it’s growing earnings at 50% per year, while a company with a P/E of 12 might be expensive if earnings are declining.

The PEG ratio (Price/Earnings-to-Growth) normalizes the P/E ratio by the company’s earnings growth rate, giving you a more meaningful comparison across companies with different growth profiles.

The Formula

PEG Ratio = P/E Ratio ÷ Annual Earnings Growth Rate (%)

Example:

  • Stock price: $200
  • EPS: $5.00
  • P/E ratio: 40x
  • Expected earnings growth: 35% per year
  • PEG ratio: 40 / 35 = 1.14

Despite the “high” P/E of 40, the PEG of 1.14 suggests the stock is reasonably priced for its growth rate.

How to Interpret PEG

PEG Range Interpretation
Under 0.5 Potentially very undervalued (verify growth is real)
0.5 to 1.0 Attractively valued relative to growth
1.0 “Fairly valued”: P/E equals growth rate
1.0 to 1.5 Slightly expensive but may be justified by quality
1.5 to 2.0 Expensive relative to growth
Over 2.0 Significantly overvalued unless growth accelerates

Peter Lynch’s rule: “The P/E ratio of any company that’s fairly priced will equal its growth rate.” In other words, PEG = 1 is “fair.”

PEG vs. P/E: A Comparison

Stock P/E Growth Rate PEG Verdict
Company A 15x 5% 3.0 Expensive (slow growth, moderate P/E)
Company B 30x 30% 1.0 Fair (high growth justifies high P/E)
Company C 25x 40% 0.63 Cheap (growth exceeds the P/E premium)
Company D 10x 8% 1.25 Slightly expensive (low P/E but also low growth)

P/E alone would rank Company D as “cheapest.” But PEG reveals Company C is actually the best value because its growth rate far exceeds its P/E premium.

Which Growth Rate to Use?

This is the most important (and debated) input in the PEG calculation:

Forward Growth Rate

Uses analyst consensus estimates for next year’s earnings growth. Most common approach.

Pros: Forward-looking, reflects expectations Cons: Analyst estimates can be wildly wrong

Historical Growth Rate

Uses actual earnings growth over the past 3-5 years.

Pros: Based on real data Cons: Past growth doesn’t guarantee future growth

Best Practice

Use the lower of forward and historical growth rates as a conservative approach. If analysts expect 25% growth but the company has historically grown at 15%, using 15-20% is more prudent.

When PEG Works Best

  1. Comparing growth stocks to each other: “Is NVDA cheaper than AMD on a growth-adjusted basis?”
  2. Technology and healthcare sectors: Where growth rates vary dramatically between companies
  3. Companies with consistent earnings growth: Predictable growth makes PEG more reliable
  4. Screening for opportunities: Filter for PEG < 1.0 to find potential undervaluation

When PEG Fails

1. Negative or Zero Growth

If earnings are declining, PEG is negative or undefined. It loses meaning entirely. Don’t use PEG for turnaround situations.

2. Very Low Growth Companies

A utility growing at 3% with a P/E of 18 has a PEG of 6.0. This doesn’t mean it’s 6x overvalued. PEG simply isn’t designed for low-growth, high-yield businesses.

3. Cyclical Companies

Cyclical companies (oil, mining, autos) have wildly fluctuating earnings. Using peak earnings growth gives a misleadingly low PEG, while using trough growth gives a misleadingly high PEG.

4. Very Small Companies

Micro-caps can show 100%+ growth rates that are unsustainable. A PEG of 0.3 based on triple-digit growth is unreliable.

Deriving Fair Value from PEG

You can reverse-engineer a fair price from PEG:

Fair Price = EPS × Growth Rate × Target PEG

Example:

  • EPS: $8.00
  • Growth rate: 20%
  • Target PEG: 1.0 (fair value)
  • Fair price: $8 × 20 = $160

If the stock trades at $120, PEG suggests it’s 25% undervalued.

PEG in a Multi-Model Framework

PEG works best as one input among many:

  1. Run a DCF analysis for the most comprehensive view
  2. Calculate the Graham Number for a conservative floor
  3. Use PEG to check if the growth premium is justified
  4. Combine results for a composite fair value

Our fair value estimates weight PEG at 25% of the composite, significant but not dominant.

Calculate PEG for Any Stock

Try our PEG ratio calculator to input your own P/E and growth assumptions, or browse stock fair value estimates where we calculate PEG-based fair values daily with real financial data.

Try It Yourself

Put this knowledge into practice with our free calculators:

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