The PEG Ratio
An attempt to price growth alongside profit by dividing the P/E by a growth rate. Useful as a rough sort, fragile as a valuation.
MadStockAlerts Research · Updated August 28, 2026
What to take away
- The PEG ratio is the P/E divided by an expected earnings growth rate in percent.
- A value near 1.0 is conventionally treated as fair, which is a convention rather than a finding.
- It is extremely sensitive to the growth rate chosen, and that rate is an estimate.
- It ignores risk and capital intensity entirely.
- Any PEG quoted without its growth input is close to uninterpretable.
MAD Academy Training Video · 0:45
Dividing by a Guess
PEG divides the P/E by a growth rate, and the growth rate is a forecast — which means the whole ratio inherits its uncertainty.
This lesson is part of a Stock Alerts + Tools plan.
The calculation
PEG = P/E / annual EPS growth rate (in percent)
- a P/E of 30 with 30 percent expected growth gives a PEG of 1.0
The intuition is reasonable: a high multiple is easier to justify when earnings are compounding quickly, and comparing two companies on the P/E ratio alone penalises the faster grower for growing.
The convention that 1.0 is fair value has no theoretical basis. It is a rule of thumb that became a benchmark by repetition, and it happens to be roughly consistent with a discounted cash flow under one particular set of assumptions and inconsistent under most others.
The fragility
The growth rate is the whole ratio, and there is no agreed way to choose it. Next year's estimate, a three-year forecast, a five-year consensus and a historical rate can produce PEGs that differ by a factor of two or more for the same company on the same day.
Two screeners reporting different PEGs for the same stock are almost always both correct on their own definitions. Any PEG quoted without its growth input is close to uninterpretable.
Scroll the chart sideways to see all of it.
What it leaves out
- Risk: growth that is certain is worth much more than growth that might not arrive, and PEG treats them identically.
- Capital intensity: growth bought with heavy reinvestment is worth less per point than growth that is free.
- Duration: five years of growth and fifteen years of the same rate are not equivalent, and neither appears.
- Balance sheet: a heavily indebted grower and a debt-free one can share a PEG.
The capital intensity omission is the most consequential. Two companies growing earnings at twenty percent, one reinvesting a tenth of its cash flow to do so and one reinvesting all of it, have identical PEG ratios and are worth very different amounts.
Where it earns its place
As a first-pass sort across a large list, PEG surfaces the cases where multiple and growth are badly out of step, which is a reasonable place to start reading.
As the basis for a valuation conclusion it is doing far more work than its inputs can support. The honest use is as a filter that decides what to examine, never as the examination.
Where the rule of one came from
The convention that a PEG of one is fair value is a rule of thumb popularised in the 1990s, not a result derived from anything. It is a rough approximation of the observation that faster-growing companies deserve higher multiples, compressed into a single number.
The approximation holds tolerably in the middle of the range and breaks at both ends. At very low growth, the ratio implies a multiple close to the growth rate, which no company trades at because a business with two percent growth is not worth two times earnings. At very high growth, it implies multiples that assume the growth persists indefinitely, which is precisely where growth rates are least durable.
The measure also ignores the risk-free rate entirely, which means it produces the same verdict on the same company whether the ten-year yield is one percent or six. Everything a discounted cash flow says about rates is absent from it.
None of that makes it useless. It is a fast screen that flags a company whose multiple is far out of line with its expected growth, and treating it as a question rather than as an answer is the reading it supports.
Whose growth estimate is in the denominator
The numerator of a PEG is observable to the cent. The denominator is a forecast, and which forecast is used changes the answer by more than most disagreements about valuation ever do.
| Source | Character | Typical bias |
|---|---|---|
| Next-year consensus | One year, widely available | Optimistic, and revised down through the year |
| Long-term growth estimate | Analysts' five-year figure | Systematically high, and rarely updated |
| Trailing realised growth | What actually happened | Backward-looking, and cyclical at the wrong moments |
| Company guidance | Management's own | Set to be beatable, where a range is given |
The second row deserves particular caution. The long-term growth estimate carried in data services is among the least maintained figures in equity research: it is often several years old, contributed by a small number of analysts, and has a well-documented upward bias. A PEG computed from it inherits all of that.
Because the ratio divides by that number, an error in it moves the output proportionally. A growth estimate that is fifty percent too high makes the PEG a third of what it should be, and nothing about the price changed.