CluenexWhat is the PEG ratio?
The PEG ratio (price/earnings-to-growth ratio) is a stock's P/E ratio divided by its expected earnings growth rate. It tries to answer a question P/E cannot: is a high price justified by fast growth?
P/E, or price-to-earnings, is the share price divided by earnings per share (EPS), the profit attributed to each share. A P/E of 40 sounds expensive. But if profits are growing 40% a year, many investors would see it differently. PEG puts price and growth into one number.
Peter Lynch, the former manager of Fidelity's Magellan Fund, popularized the idea in his 1989 book One Up on Wall Street. His rule of thumb was that a fairly priced company has a P/E roughly equal to its growth rate.
How do you calculate the PEG ratio?
Divide the P/E by the expected annual EPS growth rate, entered as a whole number. The formula is: PEG = P/E ÷ EPS growth rate (in %).
Worked example:
- Share price: $100
- EPS over the last 12 months: $4.00, so P/E = 100 ÷ 4 = 25
- Expected EPS growth: 20% a year
- PEG = 25 ÷ 20 = 1.25
The growth number can come from three places, and the choice matters:
| Growth input | Strength | Weakness |
|---|---|---|
| Next-year estimate | Most current | Most volatile |
| 3 to 5 year analyst estimate | Smoother, closer to the long-term picture | Analysts tend to be optimistic |
| Past 3 years of actual growth | Based on real results | Backward-looking |
Always check which one a website uses. Two sites can show different PEG ratios for the same stock because they use different growth inputs.
What is a good PEG ratio?
A PEG around 1.0 is the traditional benchmark for fair pricing, with lower readings looking cheaper relative to growth and higher readings looking more expensive. These bands are habits among investors, not tested laws.
| PEG | Common reading |
|---|---|
| Below 1.0 | Growth may be cheap, or the forecast may be too hopeful |
| About 1.0 | Price roughly matches growth |
| 1.0 to 2.0 | Paying a premium for growth |
| Above 2.0 | Growth looks expensive, or the forecast is low |
A very low PEG is a reason to ask questions, not a reason to celebrate. Often the market doubts the growth estimate.
How does PEG change the way you compare stocks?
PEG can flip the ranking that P/E gives you. A stock with a high P/E and fast growth may be cheaper per unit of growth than a low P/E stock that barely grows.
These three companies are made up for illustration:
| Stock | P/E | Expected EPS growth | PEG |
|---|---|---|---|
| Fast grower A | 50 | 50% | 50 ÷ 50 = 1.0 |
| Slow grower B | 15 | 5% | 15 ÷ 5 = 3.0 |
| Steady grower C | 12 | 15% | 12 ÷ 15 = 0.8 |
On P/E alone, B looks cheaper than A. On PEG, B is the most expensive of the three relative to its growth. For more on the P/E side of the comparison, see P/E ratio explained and forward P/E vs trailing P/E.
Why is the growth forecast the weak point?
The growth rate is a guess about the future, and PEG moves a lot when that guess changes. A small change in the denominator swings the result.
Take a stock with a P/E of 24. If analysts expect 24% growth, PEG is 1.0. If growth comes in at 12%, the PEG that would have been right is 2.0. The stock did not change; the forecast did.
Analyst estimates are opinions that get revised often. Read what an analyst price target really means for why forecasts deserve caution.
When does the PEG ratio fail?
PEG fails whenever earnings or growth are hard to measure or are not the main source of value. Know these cases before trusting the number.
- Slow growers. A utility growing EPS 3% with a P/E of 18 shows a PEG of 6. That says little, because investors buy it for income, not growth.
- Negative or tiny earnings. With no positive EPS there is no meaningful P/E, so PEG cannot be computed.
- One-time earnings jumps. A big gain from selling a business can inflate growth and make PEG look low. Next year growth may be negative.
- Cyclical companies. Earnings of miners, memory chip makers and similar businesses swing up and down. A low PEG at peak earnings can be a trap.
- Different industries. Typical P/E levels vary a lot by sector. The Cluenex sector benchmarks show average P/E ranging widely across sectors: 13.0x versus 33.0x. A single PEG cutoff across sectors ignores this.
- Debt and cash flow. PEG ignores the balance sheet. A company can post strong EPS growth while borrowing heavily.
EPS can also be shaped by accounting choices and buybacks. A buyback shrinks the share count, which lifts EPS even if total profit is flat. See what a stock buyback does to EPS.
How should you use PEG in a screen?
Treat PEG as a way to shorten a list, then do the real work on the survivors. A simple routine:
- Screen for a moderate PEG, such as under 1.5, inside one sector. See how to use a stock screener.
- Check where the growth number comes from. Is it next year, a multi-year estimate, or past results? How many analysts?
- Look at several years of earnings. Steady growth is more believable than one jump.
- Compare with free cash flow. If EPS rises but cash does not, be careful. See free cash flow explained.
- Check debt. Growth funded by borrowing carries more risk.
What this means for you
If you run your own brokerage account, use PEG as a question generator, not an answer. A low PEG tells you to find out why the market is skeptical. A high PEG tells you to find out what has to go right.
- Write down the P/E, the growth rate and where the growth rate came from before you rely on any PEG figure.
- Compare PEG only between companies in the same industry.
- Recalculate after each earnings report, since the forecast may have moved.
- Skip PEG for income stocks, cyclicals and companies with negative earnings.
- Confirm that earnings growth shows up as cash flow before acting on anything.
Cluenex shows a plain-English verdict and fair value range on each stock page, with the reasoning stated, which can serve as a second opinion beside your own PEG check. The method is described at https://cluenex.com/guides/how-we-value/.