What Is a P/E Ratio? How to Read the Most-Quoted Number in Investing
What price-to-earnings measures, how to calculate it, and why a "high" or "low" P/E means little on its own.
The price-to-earnings ratio, or P/E, is the most quoted valuation number in investing. On every stock page, in every earnings story and in almost every argument about whether a share is cheap or expensive, you will find it. That said, a P/E on its own tells you surprisingly little. This guide covers what the number measures and how to calculate it — and why two companies with very different P/E ratios can both be reasonably priced.
What is a P/E ratio?
A P/E ratio compares a company's share price with the profit it earns for each share. It answers a simple question: how much are investors paying today for each unit of the company's annual earnings? Take a P/E of 20: buyers are paying 20 times the profit per share that the company made over the last year.
How to calculate P/E
The formula is simple: P/E = share price ÷ earnings per share (EPS). Earnings per share is the company's net profit divided by the number of shares outstanding. Most data sites (TradeRange included) use the last twelve months of reported earnings; this version is called the trailing P/E.
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Worked example: Apple
In TradeRange data from 21 September 2026, Apple (AAPL) traded at $338.98 with a trailing P/E of 38.9. Dividing the price by the P/E gives earnings per share of about $8.71. Put another way, investors were paying almost 39 times Apple's last year of profit per share.
By dividing market capitalisation by net income, you can also calculate P/E for the whole company. The result should be close to the per-share figure. Take Nvidia: its market cap of $5.49 trillion divided by its net income of $192.9 billion gives about 28.5 — close to its reported trailing P/E of 28.7. Because share counts and reporting dates do not line up exactly, small differences creep in.
Trailing P/E vs forward P/E
The trailing P/E looks backwards; the forward P/E divides the current price by analysts' estimates of earnings over the next twelve months. When a company is expected to grow quickly, its forward P/E will sit well below its trailing P/E. Nvidia is a clear example: its trailing P/E is 28.7, but its forward P/E is 14.5. The same pattern shows up in Tesla at a different scale, with a trailing P/E of 344.3 and a forward P/E of 170.8.
Forward P/E is useful, but it depends on forecasts. On top of that, analysts' estimates can be wrong, and they often get revised after earnings reports. As a result, many investors check both numbers side by side.
What is a good P/E ratio?
There is no single good P/E. The number only makes sense when you compare it with something: the company's own history, its competitors, or the wider market. A bank and a chip designer earn money in very different ways, so the market prices their profits differently.
Trailing P/E ratios, TradeRange data as of 21 September 2026. Data is delayed.
| Company | Ticker | Sector | Trailing P/E |
|---|---|---|---|
| JPMorgan Chase | JPM | Financial Services | 15.1 |
| Coca-Cola | KO | Consumer Defensive | 26.2 |
| Microsoft | MSFT | Technology | 27.9 |
| Nvidia | NVDA | Technology | 28.7 |
| Apple | AAPL | Technology | 38.9 |
| Tesla | TSLA | Consumer Cyclical | 344.3 |
In the table, the lowest P/E belongs to JPMorgan Chase at 15.1, while Tesla's trailing P/E of 344.3 is roughly 12 times Nvidia's. A high P/E usually means investors expect profits to rise sharply. A low P/E can signal a bargain, but it can also mean the market expects earnings to shrink.
When P/E stops working
The ratio breaks down in several common situations.
- Negative earnings: if a company lost money, its P/E has no meaning. Ford currently reports a profit margin of -3.9%, so it has no published trailing P/E.
- One-off items: a large asset sale or write-down can skew a single year's profit and, with it, the P/E.
- Cyclical businesses: carmakers, miners and energy companies often look cheapest at the top of a cycle, when profits are temporarily high.
- Fast growers: a young company that reinvests everything may show tiny profits and a huge P/E for years.
Tesla puts a different spin on the last point. Its revenue grew 25.5% year on year, yet its earnings fell 3%. So its P/E is high not because profits are exploding but because the price assumes they will.
How to use P/E in practice
- Compare a company with its direct competitors, not with the whole market.
- To see what is normal for it, look at the company's own P/E over five or ten years.
- To see what growth is already priced in, check the forward P/E.
- Pair P/E with other measures such as profit margin, debt and cash flow.
Extra ratios such as PEG, which divides the P/E by the expected growth rate, can help you judge whether a high P/E is justified. P/E, forward P/E and PEG can be found for any listed company on its TradeRange stock page.
Key takeaways
- P/E = share price ÷ earnings per share.
- Trailing P/E uses last year's profit; forward P/E uses analyst forecasts.
- A P/E only means something when compared with peers, history or the market.
- Companies that lose money have no meaningful P/E.
- A high P/E is a bet on growth, not proof of it.
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Not investment advice
As of 21 September 2026, these figures are TradeRange market data and are delayed. They are meant for education only, not as investment advice. Refer to Terms and Conditions for more detail.