PEG Ratio: Adjusting the P/E for Earnings Growth

Key Takeaways

• The PEG ratio equals the P/E ratio divided by the expected percentage growth rate in earnings per share.
• A PEG near 1.0 is the classic rule-of-thumb fair value, though sector norms vary widely.
• Damodaran warns against using forward P/E in the PEG numerator because it double-counts growth.
• PEG breaks for low-growth, no-growth, and negative-earnings firms where the denominator misbehaves.

What It Is

The PEG ratio is a hybrid valuation multiple that combines a P/E multiple with an explicit growth adjustment. It exists because the bare P/E ratio penalizes high-growth firms that command rich multiples and rewards low-growth firms that look cheap on earnings alone.

Practitioners typically use a one-year, three-year, or five-year expected EPS growth rate in the denominator. The CFA Institute and Damodaran both note that the growth horizon should match the earnings number used in the P/E, and that switching horizons mid-comparison invalidates the result.

The Intuition

If two stocks both trade at a 20 P/E, but one is forecast to grow EPS at 5% and the other at 20%, the second is clearly the better value at the same multiple. PEG turns that into one number: 20 / 5 = 4.0 for the slow grower, 20 / 20 = 1.0 for the fast grower.

The 1.0 benchmark is a heuristic, not theory. Damodaran shows that the "fair" PEG depends on risk, payout, and the growth duration, so a 0.7 PEG in a stable utility is not directly comparable to a 0.7 PEG in early-stage software.

How It Works

The formula is:

PEG = P/E Ratio / Expected EPS Growth Rate (in %, not decimal)

The convention is to enter growth as a whole-number percent, not a decimal. A P/E of 20 and 15% growth gives PEG = 20 / 15 = 1.33, not 20 / 0.15.

Damodaran is explicit on a common error: if growth is measured on current earnings, use current P/E in the numerator; if on trailing earnings, use trailing P/E. Never use a forward P/E with the same forward growth rate, because the forward earnings number already incorporates the next-period growth and you would be counting it twice.

The denominator should also be the long-term growth rate, not next-year growth, when the goal is to capture the multi-year value of a high-growth firm. Most data providers use a three-to-five year analyst consensus.

Worked Example

A networking equipment company trades at $60 with trailing EPS of $2.00. Trailing P/E is 30. Sell-side analysts forecast 18% annual EPS growth over the next five years.

PEG = 30 / 18 = 1.67

A peer of the same size trades at $40 with trailing EPS of $4.00 and a 7% growth forecast. P/E = 10, PEG = 10 / 7 = 1.43.

On bare P/E the second stock looks dramatically cheaper. On PEG the gap nearly disappears: the fast-growing networking firm is paying for growth that the peer cannot match. Whether either is attractive depends on whether the growth forecasts hold and on the risk and payout assumptions behind them.

Common Mistakes

1. Mixing forward P/E with forward growth. This double-counts the next-year jump and makes high-growth firms look unrealistically cheap. Use trailing P/E with forward growth, or current P/E with current growth.
2. Using growth as a decimal. Entering 0.18 instead of 18 produces a PEG of 167 instead of 1.67. Many spreadsheets get this wrong.
3. Treating PEG as risk-adjusted. PEG ignores cost of equity entirely. A 1.0 PEG on a high-beta name is not equivalent to a 1.0 PEG on a low-beta name.
4. Applying PEG to slow growers. A utility growing EPS at 2% with a P/E of 16 produces a PEG of 8, which is statistical artifact rather than overvaluation.
5. Ignoring growth quality. Growth bought with debt, buybacks, or aggressive accounting is not the same as growth from rising revenue and stable margins. PEG cannot tell the difference.

Frequently Asked Questions

What is the PEG ratio in simple terms? It is the P/E ratio divided by the company's expected earnings growth rate as a percent. A PEG of 1.0 is the classic rule-of-thumb fair value benchmark.

How does the PEG ratio affect investment decisions? PEG lets investors compare high-growth and mature companies on the same axis. A PEG well below the sector median can flag value opportunities, while a PEG above 2 typically means the price already embeds aggressive growth expectations.

What is a real-world example of the PEG ratio? Peter Lynch popularized the PEG concept in One Up On Wall Street and used it to find growth-at-a-reasonable-price stocks at Fidelity Magellan. Damodaran's sector data shows technology PEGs commonly between 1.0 and 2.0, while utilities and banks often show PEGs above 2 because of low growth.

How can investors use the PEG ratio effectively? Match the P/E horizon to the growth horizon, use a three-to-five year EPS growth rate, and cross-check against EV/EBITDA and the cost of equity. Avoid PEG for firms growing less than 5% per year.

How is the PEG ratio different from the P/E ratio? P/E shows price per dollar of earnings; PEG divides that by expected growth. PEG is an attempt to make P/E comparable across growth rates, at the cost of depending on a forecast.

Sources

1. Damodaran, A. Chapter 18: Earnings Multiples. NYU Stern. https://pages.stern.nyu.edu/~adamodar/pdfiles/valn2ed/ch18.pdf
2. Damodaran, A. Session 18: PEG Ratio slides. NYU Stern. https://pages.stern.nyu.edu/~adamodar/podcasts/valspr21/session18slides.pdf
3. CFA Institute. Market-Based Valuation: Price and Enterprise Value Multiples. https://www.cfainstitute.org/insights/professional-learning/refresher-readings/2026/market-based-valuation-price-enterprise-value-multiples
4. Mauboussin, M. and Callahan, D. Valuation Multiples. Morgan Stanley Counterpoint Global Insights. https://www.morganstanley.com/im/publication/insights/articles/article_valuationmultiples.pdf

Disclaimer

This article is educational content only and is not financial advice. Nothing here is a recommendation to buy, sell, or hold any security. Consult a licensed advisor before making investment decisions.