A P/E of 30 with 30% growth isn't expensive?
High-P/E growth stocks are often defended with "it's not expensive given the growth." The PEG ratio puts that argument into a number: the P/E divided by the earnings growth rate in percent. A P/E of 30 with 30% annual growth gives a PEG of 1.
PEG is an intuitive starting point for comparing companies growing at different speeds, but its denominator is a forecast, and that makes it fragile. This guide explains the calculation, shows how much the growth assumption moves the result, and covers matching time periods and avoiding base effects, using hypothetical numbers.
How PEG is calculated
PEG equals the P/E ratio divided by the annual growth rate of earnings per share, in percent. FINRA's guide describes P/E as the share price divided by EPS; PEG adds a second division to account for growth. A value around 1 is often cited as a reference point, but that is a rule of thumb, not a theoretically correct level.
Which growth rate goes in the denominator matters most. It could be the past three years' actual growth or analysts' forecasts for the next three to five years. The same company's PEG can differ by a factor of two or three depending on that choice, so always compare companies on the same basis.
How the growth assumption changes PEG
The table below applies different growth assumptions to a hypothetical company trading at 30 times earnings.
| Scenario | Assumed annual EPS growth | PEG | Reading |
|---|---|---|---|
| Optimistic | 40% | 0.75 | Looks cheap for its growth |
| Base | 30% | 1.00 | Near the reference point |
| Cautious | 15% | 2.00 | Looks expensive for its growth |
| Slowdown | 8% | 3.75 | Hard to justify by growth |
With the price and P/E unchanged, changing only the growth assumption moves PEG from 0.75 to 3.75, a fivefold range.
Base effects and matching periods
After a year of collapsed earnings, the following year's growth rate looks abnormally high. As a hypothetical example, if EPS falls from $2.00 to $1.00 and then recovers to $2.00, growth is 100%. A PEG built on that number looks very low, even though earnings have only returned to where they were.
Multi-year average growth is therefore more stable than a single year. The period behind the P/E (trailing or forward) should also match the period behind the growth rate; dividing a forward P/E by historical growth mixes numbers from different points in time.
Forecast uncertainty
Future growth rates usually come from analyst estimates or company guidance. These are revised often as conditions, competition, and execution change, and long-term three-to-five-year estimates in particular can miss by a wide margin. If estimates lean optimistic, PEG will look more attractive than it should.
PEG also ignores the quality of growth. EPS growth from buybacks, from expanding the business, or from heavy borrowing all count the same. Whenever you look at a growth rate, check where that growth comes from.
Consider two hypothetical companies, each with a P/E of 24 and forecast EPS growth of 24%, so both have a PEG of 1. The first grows net income 24% from rising sales; the second grows net income 10% and shrinks its share count with debt-funded buybacks. The PEG is identical, but the second company's growth is both slower and riskier.
A checking routine
When calculating PEG, or reviewing one someone else presents, use the company's filings and the steps below. Investor.gov's guide to the 10-K shows where the EPS figures and the MD&A discussion of results sit.
- Confirm whether the P/E uses trailing four-quarter or forecast earnings, and basic or diluted EPS.
- Confirm whether the growth rate is historical or forecast, and over how many years it is averaged.
- Look at three to five years of EPS to make sure a depressed base year is not inflating growth.
- Use the EPS note to split growth into net income growth and share-count reduction.
- Recalculate PEG under optimistic, base, and cautious growth scenarios to see how sensitive the conclusion is.
Limits of PEG
PEG compresses a company's value into one growth rate, so it ignores risk, capital efficiency, and how long growth lasts. Thirty percent growth that ends after two years is worth far less than thirty percent that continues for a decade.
The figures here are hypothetical. For real decisions, use the latest filings and estimates with their dates, and treat PEG as a way to ask how much growth the current price assumes rather than as a verdict.