PEG Ratio

The PEG ratio formula is straightforward:

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

The P/E ratio is the stock's current price divided by its earnings per share. The growth rate is typically the expected EPS growth rate over the next 1-3 years.

Example calculation:

Stock XYZ trades at $75 with EPS of $3.00. Its P/E ratio is 25. Analysts expect EPS to grow at 20% annually over the next 3 years. PEG = 25 / 20 = 1.25.

Which growth rate to use matters:

Forward PEG (most common): Uses the consensus analyst estimate for future EPS growth, typically 1-3 year forward estimates. This is the standard version used by most financial data providers. The limitation: analyst estimates are often wrong, especially for cyclical companies and companies in transition.

Trailing PEG: Uses the actual historical EPS growth rate over the past 1-3 years. More reliable because it uses real data, but backward-looking. A company whose growth is accelerating will look expensive on trailing PEG but may be cheap on forward PEG.

5-year PEG: Uses a 5-year forward growth estimate. Smooths out year-to-year volatility but relies on longer-term projections that are inherently less reliable.

Peter Lynch, who popularized the PEG ratio in his book One Up on Wall Street, used a simple rule: a fairly valued stock has a PEG of approximately 1.0. Any stock with PEG well below 1.0 deserves closer attention.

PEG gives you a single number that adjusts valuation for growth. Here is how to interpret it:

PEG below 0.5: Potentially significantly undervalued relative to growth. Either the market is missing the growth story, or the growth estimate is too optimistic. Investigate which one. If the growth is real, this can be a compelling value opportunity.

PEG 0.5 to 1.0: Potentially undervalued. The stock is priced below what its growth rate would justify. This is the sweet spot for growth-at-a-reasonable-price (GARP) investors.

PEG around 1.0: Fairly valued. The market is pricing in the expected growth accurately. Not cheap, not expensive. Peter Lynch considered PEG of 1.0 to be fair value for a growth stock.

PEG 1.0 to 1.5: Moderately expensive relative to growth. May still be worth holding if the company has other advantages (competitive moat, recurring revenue, margin expansion potential).

PEG above 2.0: Expensive relative to growth. The stock is priced as if growth will be faster than current estimates, or the market is paying a premium for quality, brand, or safety.

Important context: PEG thresholds vary by market environment. During periods of low interest rates, the market tolerates higher PEG ratios because the discount rate on future earnings is lower. During high-interest-rate environments, PEG expectations compress — even PEG of 1.0 may be considered expensive.

The P/E ratio and PEG ratio answer different questions:

P/E answers: How much am I paying for each dollar of current earnings? PEG answers: How much am I paying for each dollar of current earnings, adjusted for how fast those earnings are growing?

When P/E is sufficient: For mature, stable-growth companies where earnings growth is predictable and similar across peers (utilities, consumer staples, REITs). A utility growing at 3% with a P/E of 15 vs. another growing at 3% with a P/E of 12 — P/E alone tells you which is cheaper.

When PEG is essential: For comparing growth companies where growth rates differ significantly. A software company growing at 40% with a P/E of 60 vs. a retailer growing at 8% with a P/E of 20 — P/E makes the software company look 3x more expensive, but PEG shows the software company (PEG 1.5) is actually cheaper on a growth-adjusted basis than the retailer (PEG 2.5).

Neither metric works for: Companies with negative earnings (use EV/Revenue), cyclical companies at peak earnings (P/E looks artificially low), or turnaround situations where past growth is irrelevant to future prospects.

PEG is a useful screening tool, but it has important limitations that can lead to bad decisions if ignored:

Growth estimates are guesses. The PEG denominator relies on analyst projections that can be wildly wrong. Analysts tend to extrapolate recent trends: they overestimate growth for hot stocks and underestimate recovery for beaten-down ones. Always check whether consensus estimates look reasonable, not just the resulting PEG number.

PEG does not work for cyclical companies. Cyclical businesses (oil, mining, autos, semiconductors) have earnings that swing dramatically with the economic cycle. At the peak of the cycle, earnings are high and P/E is low, making PEG look attractive — right before earnings collapse. At the trough, earnings are depressed and P/E is high, making PEG look terrible — right before recovery.

PEG ignores risk and quality. A company growing at 30% through acquisition-fueled debt is riskier than one growing at 30% organically. Both might show PEG of 1.0, but the organic grower deserves a premium. PEG treats all growth as equal — it is not.

Negative earnings break the formula. If a company has negative EPS, P/E is negative and PEG is meaningless. For pre-profit companies, use EV/Revenue or other metrics.

Growth rate denominator inconsistency. Some data providers use 1-year forward growth, others use 3-year or 5-year CAGR. The same stock can show PEG of 0.8 or 1.6 depending on which growth estimate is used. Always check which growth period your data source uses before comparing PEG ratios across platforms.