P/E Ratio: What It Does Say About a Stock, What It Doesn't, and Why 40 Isn't Always Expensive

Price to Earnings (P/E) ratio is the share price divided by earnings per share for the year. A stock at $100 with a profit of 5 dollars per share trades at a multiple of 20$: the market is paying twenty years of current earnings for every share. This is the most common number in the investing world, and also the easiest to misread, because it looks like an answer ("expensive" or "cheap") when it's really just a question: why is the market willing to pay so much, or so little, for this profit.

For a technical trader, the P/E ratio isn't a timing tool, and we won't try to turn it into one. But it's context: it explains why a given stock reacts the way it does to earnings reportsand why a "growth stock" and a "value stock" behave differently in the same market. And that's a good reason to understand it correctly.

Trailing vs. forward: same name, two numbers

Trailing P/E divides the price by the earnings of the last four quarters already reported. A fact, not an estimate. Forward P/E divides the price by the earnings analysts forecast for the coming year. An estimate, not a fact. In a fast-growing company, the forward P/E is much lower than the trailing one, because the denominator is growing; in a company whose profits are shrinking, it's the opposite.

When one site says a stock is at a multiple of 45 and another says 28that's usually the difference. Both are correct, and they're answering different questions. On TechAnalyzer's analysis screen, both are shown side by side, along with the multiples of direct competitors, because a P/E without comparison is a number without meaning.

Why you only compare within the same industry

A multiple of 12 is expensive for a bank and cheap for a software company. The difference isn't a market mistake, it's the growth expectation: investors pay more for earnings expected to double within five years than for earnings expected to stay flat. Entire industries trade at different multiples because their growth, earnings stability, and capital needs differ. Utilities (electricity, water) and banks typically trade at single-digit to low-teens multiples; technology and pharmaceuticals trade at much higher ones; cyclical companies (energy, commodities) swing between extremes depending on the business cycle.

So the only comparison that means something is a stock against its competitors and against its own history. "Nvidia at a multiple of 40" says little; "Nvidia at a multiple of 40 when competing manufacturers are at25, and two years ago it itself was at60" starts to be information.

PEG: the multiple divided by growth

To correct for the growth bias, investors use PEG: the P/E ratio divided by the expected annual earnings growth rate (in percent). A stock at a multiple of 40 growing 40% a year has a PEG of 1; a stock at a multiple of 15 growing 5% has a PEG of 3. According to the rough rule that Peter Lynch made famous, a PEG around 1 is "fair," and above it is expensive. This is a rule of thumb, not a law: it assumes the projected growth will materialize, and that's exactly the assumption that breaks down most often.

When the multiple simply says nothing

• Negative earnings: There's no multiple. A company that's losing money shows "N/A" or a meaningless negative number. Most young growth companies fall into this category, and they're valued using the sales multiple (P/S) or cash flow.
• One-time profit: Sale of a division, tax credit, asset revaluation. Earnings per share spike for one year, the multiple "shrinks" to6, and the stock looks cheap while the business itself hasn't changed. The opposite also happens with a one-time loss.
• Cyclical companies at the peak of the cycle: A memory-chip manufacturer or an energy company in a peak year shows huge profit and a multiple of 5. That's not "cheap" — it's the market saying this profit is temporary. At the trough of the cycle, the same company shows a multiple of 50 on tiny profit, even though it's actually cheap. With cyclicals, the multiple works opposite to intuition.
• Stocks with "adjusted" earnings: Tech companies sometimes present "Non-GAAP" earnings that exclude stock-based compensation and other items. The multiple on adjusted earnings is much lower than the multiple on accounting earnings. When comparing, you need to make sure you're comparing the same type of earnings.

How a technical trader uses the multiple without turning into a value investor

Technical analysis asks what the market is doing with the price right now; the multiple asks how much the business is worth. These are different questions, and a swing trader doesn't need the answer to the second to answer the first. But three modest uses of the multiple do help even those trading charts:

• Understanding sensitivity to earnings reports: A stock at a multiple of 60 is priced for future growth, and any small miss in guidance hits it hard. A stock at a multiple of 10 with a stable dividend moves less on the same report. The multiple tells you how "stretched" the price is before the event, and therefore how much of a gap to expect.
• Distinguishing between types of stocks in the same setup: A breakout in a value stock at a multiple of 9 and a breakout in a growth stock at a multiple of 80 are the same pattern on the chart with very different behavior afterward, especially during periods when the market shifts preference between "growth" and "value." You won't always know in advance which period it is, but you'll at least know which side you're on.
• Not arguing with the chart because of the multiple: "It's at a multiple of 90, it has to come down" is the argument behind many shorts that got wiped out. A stock can stay "expensive" for years as long as growth justifies it, and "cheap" for years when it's cheap for a reason. Technicals tell you when; the multiple only tells you how much, and even that only by comparison.