PEG is a shortcut with a very large assumption inside it
PEG divides a P/E multiple by an earnings-growth rate. It attempts to answer: “How much valuation am I paying relative to the growth rate I expect?” The weakness is that the growth estimate can dominate the result.
Worked example
At 30× earnings and 30% expected EPS growth, the common shorthand gives PEG = 1.0. If expected growth is revised to 20%, PEG becomes 1.5 without the share price changing.
What PEG ignores
- How long growth can last
- Returns on incremental capital
- Cash conversion
- Debt and financial risk
- Margin durability
- Cyclicality
- Quality of the forecast
Growth quality matters
Two companies can both grow EPS 25%, while one needs huge incremental capital and the other converts most incremental profit into cash. A single PEG cannot distinguish them.
Historical PEG
Using realised historical growth can be less dependent on forecasts but may describe a growth regime that has already ended. Forecast PEG is forward-looking but more uncertain.
Better workflow
- Calculate the multiple.
- Document the growth assumption and source.
- Test several growth cases.
- Check ROCE, margins and cash conversion.
- Ask what growth is already embedded in the price.
Checklist
- Growth period defined
- Forecast source recorded
- Scenario range tested
- Growth durability tested
- Capital requirements tested