P/E Ratio Explained: How to Tell If a Stock Is Cheap or Expensive (With Examples)
Updated October 2026 · 11 min read
Is a $500 stock expensive? Is a $15 stock cheap? Most beginners judge a stock by its share price, but the price alone tells you almost nothing. A $500 stock can be a bargain, and a $15 stock can be wildly overpriced.
What matters is how much you pay compared with what the company actually earns. The most widely used tool for measuring that is the price-to-earnings ratio, or P/E ratio. You'll see it on every stock quote page, in every earnings story, and in almost every conversation about whether the market is "too high."
This guide explains what the P/E ratio means, how to calculate it, how to use it to compare stocks, and the traps that catch investors who rely on it alone.
Key takeaways
- The P/E ratio shows how many dollars investors pay for each $1 of a company's yearly earnings.
- Trailing P/E uses the past 12 months of earnings; forward P/E uses analysts' estimates for the next 12 months.
- As of early October 2026, the S&P 500's forward P/E was 19.0, close to its 10-year average of 19.1.
- Compare P/E ratios within the same industry, and against a company's own history and growth rate.
- A low P/E isn't automatically a bargain. It can signal shrinking or unusually high earnings.
In this guide:
- What is the P/E ratio?
- Trailing P/E vs. forward P/E
- What is the market's P/E right now?
- How to use P/E to compare stocks
- The PEG ratio: adding growth to the picture
- A three-company example
- When the P/E ratio misleads you
- A simple P/E checklist
- Frequently asked questions
What Is the P/E Ratio?
The P/E ratio compares a company's share price with its earnings per share (EPS). EPS is the company's net profit divided by the number of shares outstanding.
P/E ratio = Share price ÷ Earnings per share
Example: A company's stock trades at $100, and it earned $5 per share over the past year. Its P/E ratio is $100 ÷ $5 = 20.
That means investors are paying $20 for every $1 the company earns in a year. Another way to see it: if earnings stayed flat forever, it would take 20 years of profits to "earn back" the price you paid for a share.
The Flip Side: Earnings Yield
If you turn the P/E ratio upside down, you get the earnings yield: EPS ÷ price. For our example, $5 ÷ $100 = 5%. This makes it easy to compare a stock with other investments. If a savings account pays 4% and a stock's earnings yield is 5%, the stock offers only a little more in earnings, and with much more risk. Investors accept that because they expect the company's earnings to grow.
Why Share Price Alone Means Nothing
Compare two companies:
- Company A trades at $500 with EPS of $25. P/E = 20.
- Company B trades at $15 with EPS of $0.30. P/E = 50.
Company B's shares look "cheap," but relative to its earnings, it's two and a half times as expensive as Company A. A low share price usually just means the company has more shares outstanding, not that it's a better deal.
Trailing P/E vs. Forward P/E
When you see a P/E ratio, check which earnings it uses. There are two main versions:
| Trailing P/E (TTM) | Forward P/E | |
|---|---|---|
| Earnings used | Actual EPS from the last 12 months | Analysts' estimated EPS for the next 12 months |
| Strength | Based on real, reported results | Looks ahead, which is what stock prices do |
| Weakness | Can be outdated if the business is changing fast | Estimates can be wrong, often too optimistic |
| Where you'll see it | Most stock quote pages ("P/E (TTM)") | Analyst reports and market commentary |
Example: A stock trades at $60. Last year it earned $3 per share, and analysts expect $4 next year. Its trailing P/E is 20 ($60 ÷ $3), but its forward P/E is just 15 ($60 ÷ $4). When a company's earnings are growing, the forward P/E is lower than the trailing P/E.
What Is the Market's P/E Right Now?
The P/E ratio isn't only for single stocks. Analysts also calculate it for entire indexes, which helps you judge whether the market as a whole looks expensive or reasonable.
According to FactSet's October 2, 2026 Earnings Insight report, the S&P 500 had a forward 12-month P/E ratio of 19.0. That was below its 5-year average of 19.8 and just below its 10-year average of 19.1. The trailing 12-month P/E was 25.7, above its 5-year average of 24.4 (FactSet).
The big gap between those two numbers tells a story: analysts expect earnings to rise substantially over the next year. If those expectations come true, today's prices look roughly in line with recent history. If earnings disappoint, the market looks more expensive than the forward P/E suggests.
FactSet's report also shows how much P/E ratios vary by industry. The Consumer Discretionary (22.6) and Industrials (22.5) sectors had the highest forward P/E ratios, while Energy (13.0) and Financials (14.1) had the lowest. That's why comparing a bank with a retailer by P/E alone doesn't tell you much.
If you own an S&P 500 fund, like those covered in our index funds for beginners guide, this is the P/E ratio of what you own.
How to Use P/E to Compare Stocks
A P/E ratio means little on its own. It becomes useful when you compare it with the right benchmark. Here are three comparisons that work.
1. Compare With Industry Peers
Companies in the same industry tend to have similar growth rates and risks, so their P/E ratios are more comparable. If most large banks trade around 12 to 14 times earnings and one trades at 9, it's worth asking why. Is it a bargain, or does it have a problem the others don't?
2. Compare With the Company's Own History
A company that has traded between 15 and 20 times earnings for a decade and now trades at 30 has become more expensive by its own standards. That might be justified by faster growth, or it might be excitement that will fade.
3. Compare With the Company's Growth
Fast-growing companies usually deserve higher P/E ratios, because their earnings will be much larger in a few years. That leads to one of the most useful refinements of P/E: the PEG ratio.
The PEG Ratio: Adding Growth to the Picture
The PEG ratio divides the P/E ratio by the company's expected annual earnings growth rate (as a whole number).
PEG ratio = P/E ratio ÷ Annual EPS growth rate (%)
A PEG around 1 is often seen as a fair balance between price and growth. Below 1 may suggest the stock is cheap for its growth; well above 1 may suggest you're paying a lot for it.
- Company X: P/E of 30, earnings expected to grow 25% a year. PEG = 30 ÷ 25 = 1.2.
- Company Y: P/E of 12, earnings expected to grow 3% a year. PEG = 12 ÷ 3 = 4.0.
Company X has a P/E more than twice as high, yet it may be the better value once growth is considered. Keep in mind that the PEG ratio depends on growth estimates, which can easily be wrong.
A Three-Company Example
Let's put everything together with three made-up companies. Each one has a different story behind its P/E.
| Company | Price | EPS | P/E | Expected growth | PEG |
|---|---|---|---|---|---|
| Steady Power Utility | $54 | $3.00 | 18 | 4% | 4.5 |
| CloudScale Software | $140 | $4.00 | 35 | 30% | 1.2 |
| Ironworks Steel | $48 | $8.00 | 6 | −40% | n/a |
Hypothetical companies for illustration only.
Steady Power Utility looks moderately priced at 18 times earnings. But with only 4% growth, its PEG of 4.5 shows you're paying a full price for a slow business. Investors often accept that for utilities because their earnings and dividends are very stable.
CloudScale Software has the highest P/E at 35, which scares many beginners. Yet its PEG of 1.2 suggests the price is fairly reasonable for 30% growth, as long as that growth actually happens.
Ironworks Steel looks like the bargain of the group at just 6 times earnings. But analysts expect its earnings to fall 40% as steel prices come down from a peak. This is the classic value trap, which we'll look at next.
When the P/E Ratio Misleads You
The P/E ratio is a starting point, not a verdict. Here are the most common ways it can point you in the wrong direction.
The Cyclical Trap
Companies in cyclical industries, like steel, oil, airlines and homebuilders, earn the most at the top of their cycle. That's exactly when their P/E ratios look lowest.
Return to Ironworks Steel. It earns $8 per share at the peak, and its P/E is 6. Next year, earnings drop to $2 per share and the stock falls to $30. Its P/E has risen to 15, even though the share price fell 37.5%. The "cheap" stock was cheap for a reason.
Other Situations Where P/E Falls Short
- No profits, no P/E. If a company loses money, it has no meaningful P/E ratio. Many quote pages show "N/A" or a dash. You'll need other measures, such as price-to-sales.
- One-time items. A big asset sale can inflate earnings for a year and make the P/E look artificially low. A large one-time charge can do the opposite.
- Debt is invisible. P/E ignores how much a company owes. Two companies with the same P/E can carry very different levels of risk. Professionals often also check measures like EV/EBITDA, which include debt.
- Accounting differences. Some quotes use GAAP earnings; others use "adjusted" earnings that exclude certain costs. Make sure you're comparing the same kind of number.
A Simple P/E Checklist
Before you decide a stock is cheap or expensive, walk through these steps:
- Find both P/E ratios. Look up the trailing and forward P/E on your broker's quote page or a free financial site.
- Check that earnings are positive and normal. Look for losses, one-time gains or a cyclical peak.
- Compare with 3 to 5 industry peers. Is the stock above, below or in line with similar companies?
- Compare with its own 5- or 10-year range. Is it trading at the high or low end of its history?
- Divide by the growth rate. Calculate the PEG ratio to see whether growth justifies the price.
- Look beyond P/E. Review debt, cash flow and the business itself before you buy.
If you're still learning how to place your first trade, our guide to starting stock trading covers the basics, from choosing a broker to understanding order types.
5 Common P/E Mistakes
- Buying a stock just because its P/E is low. Low P/E stocks are often cheap for good reasons, like shrinking earnings or a weak business.
- Avoiding every high P/E stock. Some of the best-performing companies have traded at high P/E ratios for years because their earnings kept growing fast.
- Comparing across industries. A software company at 30 and a bank at 12 aren't directly comparable.
- Trusting forward estimates blindly. Analysts' forecasts can change quickly, especially in a slowing economy.
- Using P/E to time the market. A high market P/E can stay high for years. It's a better guide to long-term expected returns than to next month's moves.
Frequently Asked Questions
What is a good P/E ratio?
There's no single good number. It depends on the industry, the company's growth and interest rates. A useful starting point is to compare a stock's P/E with its industry peers and with the S&P 500's forward P/E, which was 19.0 in early October 2026.
Is a high P/E ratio bad?
Not necessarily. A high P/E means investors expect strong future growth. It becomes a problem when that growth doesn't happen, because the stock price can fall sharply when expectations are reset.
What does a negative P/E ratio mean?
It means the company lost money over the period measured. Most financial sites show "N/A" instead of a negative number, because a P/E based on losses isn't useful for valuation.
Where can I find a stock's P/E ratio?
Your brokerage app's quote page almost always shows it, usually labeled "P/E (TTM)." Free financial websites list both trailing and forward P/E ratios, along with the EPS figures used to calculate them.
Do ETFs and index funds have a P/E ratio?
Yes. Fund providers and financial sites often list a weighted average P/E for the stocks a fund holds. It's a quick way to see whether a fund leans toward expensive growth stocks or cheaper value stocks.
The Bottom Line
The P/E ratio answers one simple question: how much are you paying for each dollar a company earns? That makes it one of the fastest ways to tell whether a stock looks cheap or expensive.
But a P/E ratio only becomes meaningful in context. Compare it with industry peers, with the company's own history and with its growth rate. Watch out for cyclical peaks, one-time items and companies without profits. Used that way, the P/E ratio won't make your decisions for you, but it will help you ask the right questions before you buy.
Disclaimer: This article is for educational purposes only and is not financial advice. Companies in the examples are fictional. Market data is as of the date cited and will change. Consider your own situation or consult a licensed financial professional before investing.
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