PEG Ratio Explained
How the PEG ratio adjusts P/E for growth, with worked examples.
⏱️ ~6 min read
Key Takeaways
- PEG Ratio = P/E Ratio ÷ Expected Annual Earnings Growth Rate (as a number, not a percentage)
- It attempts to answer: is this P/E reasonable given how fast earnings are expected to grow?
- A PEG around 1.0 is sometimes referenced as a rough 'fair value' benchmark, though this is a simplification, not a rule
- PEG depends heavily on the growth estimate used, which is itself uncertain and can vary between sources
The problem PEG tries to solve
The P/E ratio alone doesn't account for how fast a company's earnings are expected to grow. Two companies could have the same P/E of 30, but if one is expected to grow earnings 10% per year and the other 30% per year, paying the 'same price' for each dollar of current earnings means very different things for their future trajectories.
The price/earnings-to-growth (PEG) ratio attempts to adjust for this by dividing the P/E ratio by an expected earnings growth rate, producing a single number intended to be more comparable across companies with different growth profiles.
The formula
PEG Ratio = P/E Ratio ÷ Annual EPS Growth Rate (expressed as a whole number, not a decimal — e.g., use '15' for 15% growth, not '0.15').
Example: Comparing two companies with PEG
Company A: P/E = 30, expected annual earnings growth = 30%. PEG = 30 ÷ 30 = 1.0.
Company B: P/E = 30, expected annual earnings growth = 10%. PEG = 30 ÷ 10 = 3.0.
Even though both companies have the same P/E, Company A's PEG suggests its valuation is more in line with its growth expectations, while Company B's higher PEG suggests its price may be elevated relative to its expected growth — at least based on these particular growth estimates.
The 'PEG of 1' rule of thumb
A PEG ratio around 1.0 is sometimes referenced informally as a rough indicator that a stock's P/E is 'in line' with its growth rate — a PEG meaningfully below 1 might suggest the stock is cheap relative to its growth, and meaningfully above 1 might suggest it's expensive relative to its growth.
This 'rule of thumb' is a simplification that doesn't hold universally — it doesn't account for differences in risk, profitability, interest rates, or how sustainable a given growth rate actually is. It's best treated as a rough screening tool rather than a precise valuation method.
The challenge of the growth rate input
PEG is highly sensitive to the growth rate used — and growth rates are estimates, not facts. Different sources may use different time horizons (next year vs. next five years) or different methodologies (analyst consensus estimates vs. historical growth rates), producing different PEG values for the same company.
A company whose earnings growth is expected to slow down significantly after a near-term burst (or accelerate after a temporary slowdown) can have a PEG that looks attractive or unattractive depending entirely on which period's growth rate is used in the calculation.
Using PEG alongside other tools
PEG can be a useful complement to P/E, particularly when comparing companies with meaningfully different growth profiles within the same industry — but like any single ratio, it works best as part of a broader analysis that also considers profitability, balance sheet strength, competitive position, and the reliability of the growth estimates being used.
Frequently Asked Questions
Can PEG be negative?+
Yes, if either the P/E or the growth rate is negative (e.g., a company with negative earnings, or one expected to see earnings decline) — a negative PEG isn't generally meaningful in the same way a positive PEG is, and is usually not used for comparison in that case.
Which growth rate should I use — past or future?+
Both can be used and serve different purposes: historical growth shows what has actually happened, while projected future growth (often based on analyst estimates) reflects expectations going forward — and it's the future that ultimately determines whether a current price turns out to have been reasonable.
Does a low PEG guarantee a good investment?+
No — it suggests a stock's valuation may be reasonable relative to its growth estimate, but the growth estimate itself could be wrong, and PEG doesn't account for other important factors like financial health, competitive risks, or overall market conditions.