Why a PEG Ratio of 1 or Less Does Not Establish Undervaluation
PEG divides P/E by earnings growth, but does not fully adjust for growth duration, quality, or risk. Learn to align growth assumptions and recognize distortions from losses and low earnings bases.
PEG divides PER by the percentage number representing expected EPS growth. A figure below 1 does not establish undervaluation; you must also check whether growth duration, risk, and the capital needed for growth are comparable. Growth calculated from losses or earnings near zero requires particular care.
Align percentage units and growth periods first
With PER of 20x and EPS growth of 25%, PEG is 20 ÷ 25 = 0.8. Entering growth as the decimal 0.25 produces 80, which uses a different unit convention from standard PEG reporting. The period matters even more than the units. A rebound over the next year is not the same growth expectation as a compound annual growth rate over several years. Also record whether the EPS reference point in the PER denominator aligns with the starting EPS used for growth. Using next-year EPS that already incorporates growth to calculate a lower PER, then applying the high growth rate from the previous year again, can count the growth effect twice.
The same growth rate can require different investment
A business that needs substantial new factories and inventory to increase earnings by 20% leaves shareholders with different cash than one that can use existing facilities and customer relationships. PEG does not directly include reinvestment. Dividing by growth also does not equalize debt risk, customer concentration, or dividend capacity. For comparisons, break down the sources of growth into volume, price, margins, and share-count changes, and assess whether the result converts into cash. Even for the same EPS growth, distinguish a smaller denominator from share repurchases from growth in business earnings.
Stop relying on the calculation when base effects dominate
If prior-year EPS was temporarily very low, even a modest recovery can produce a high percentage growth rate. Conversely, when a mature company’s growth is near 0%, PEG can soar or become undefined. A negative PEG caused by negative growth does not mean the company is cheap. In these cases, also examine PER based on normalized EPS or a valuation range based on cash flow. Record the source and preparation date of the growth forecast, and recalculate how much PEG changes when estimates for the same company are reduced.
Worked example
Hypothetical example: With PER of 24x and forecast compound annual EPS growth of 30%, PEG is 0.8. Reducing only the growth estimate to 15% raises PEG to 1.6 even with the share price unchanged. Using the 100% increase from a one-year EPS recovery from KRW 100 to KRW 200 produces 0.24, but that recovery cannot be assumed to repeat for several years. None of these three results can mechanically serve as a buy criterion.
What to check
- Have you entered growth as a percentage number?
- Have you aligned the earnings reference point in PER with the starting point for growth?
- Does the high growth rate result from a temporary recovery or a falling share count?
- Have you also considered the investment and financing needed for growth?
Sources and primary materials
This is educational material about research methods. For an actual company decision, verify the filings and primary sources for the relevant period.