Quick answer
The P/E ratio is a company's share price divided by its earnings per share. A P/E of 20 means investors pay $20 for each $1 of yearly profit. It is most useful for comparing similar companies or a company with its own past [1] [2].
Key points
- P/E = share price ÷ earnings per share (EPS).
- Trailing P/E uses the last 12 months of actual earnings; forward P/E uses estimates for the next 12 months.
- Earnings yield is the P/E flipped over: EPS ÷ price.
- P/E is most useful within the same industry, since fast-growing firms tend to carry higher P/Es.
- A low P/E is not automatically cheap, and P/E is meaningless when earnings are negative.
#How do you calculate the P/E ratio?
Start with earnings per share (EPS): a public company's net profit divided by the number of its common shares [3]. FINRA's example is a company with $100 million of net income and 50 million shares outstanding, which gives EPS of $2 [2]. Then divide the share price by EPS. Investor.gov describes the P/E ratio as a way of gauging whether a stock price is high or low compared with the past or with other companies, and calculates it using earnings for the past 12 months [1].
In code the whole thing is one line: pe = price / eps. FINRA's own illustration is a stock at $100 with EPS of $5, which has a P/E of 20 [2]. Put another way, FINRA says P/E tells you how much investors are paying for a dollar of a company's earnings [4]. The earnings per share entry covers basic and diluted EPS, and the P/E ratio calculator does the arithmetic for you.
Worked example
One stock, two P/E ratios
A hypothetical company trades at $60. Its EPS over the last four quarters was $0.70, $0.75, $0.72 and $0.83. Analysts estimate EPS of $4.00 for the next 12 months.
- Trailing 12-month EPS (0.70 + 0.75 + 0.72 + 0.83)
- $3.00
- Trailing P/E ($60 ÷ $3.00)
- 20.0
- Forward P/E ($60 ÷ $4.00 estimate)
- 15.0
- Trailing earnings yield ($3.00 ÷ $60)
- 5.0%
- Forward earnings yield ($4.00 ÷ $60)
- 6.67%
The same share price produces a P/E of 20 or 15 depending on which earnings you use. Always check which one a website is quoting.
Hypothetical figures, calculated in Python. The forward figure depends on an estimate that may turn out wrong.
#What is the difference between trailing and forward P/E?
Trailing P/E uses earnings already reported, usually the last four quarters, sometimes labelled TTM (trailing twelve months) [5]. Forward P/E uses estimates of earnings expected over the next four quarters [5]. Trailing P/E rests on actual results but looks backward; forward P/E looks ahead but rests on forecasts that can be revised or missed. Some data providers also blend the two, combining two actual quarters with two estimated ones [5].
| Trailing P/E | Forward P/E | |
|---|---|---|
| Earnings used | Last 4 reported quarters | Estimates for the next 4 quarters |
| Based on | Actual, reported results | Analyst or company forecasts |
| Strength | Uses real numbers | Reflects expected changes |
| Weakness | May miss a recent turning point | Estimates can be wrong or revised |
#What is earnings yield?
Earnings yield is the P/E ratio turned upside down: EPS divided by price, shown as a percentage. A P/E of 20 is an earnings yield of 5%, because $1 of earnings divided by $20 of price is 0.05. Some investors find it easier to read because it looks like an interest rate, which makes it simple to set beside a bond yield. It is not cash in your pocket, though: most of a company's earnings may be reinvested rather than paid out as dividends.
#What counts as a high or low P/E?
There is no single right number. FINRA notes that P/E is generally used to compare companies in the same industry, and that fast-growing companies tend to have higher P/E ratios while firms in mature, slow-growth industries tend to have lower ones [2]. Comparing a software company's P/E with a utility's tells you more about their industries than about which is a better buy.
P/E ratios of four hypothetical stocks
#Why can the P/E ratio mislead you?
P/E has real limits. The earnings figure is an accounting measure that can be affected by one-off items or by choices in how profit is reported, and data sites may mix GAAP reported earnings with adjusted operating earnings [5]. When earnings are very small the ratio becomes huge, and when they are negative it is not meaningful at all [5].
A low P/E can also be a trap. FINRA warns that not every stock with a low P/E represents true value, because sometimes stocks sell off due to a deterioration in their fundamentals that is not yet commonly understood [6]. Before relying on any ratio, read the numbers behind it — our guide to reading financial statements shows where EPS comes from.
Common beginner mistakes
Judging value by share price alone
A $5 share can be far more expensive per dollar of earnings than a $500 share. Compare P/E, not price tags.
Comparing P/Es across unrelated industries
Fast-growing sectors usually carry higher P/Es than mature ones. Compare a company with its peers or its own history.
Mixing trailing and forward figures
A forward P/E of 15 and a trailing P/E of 20 can describe the same stock on the same day. Use the same type when comparing.
Treating a low P/E as a bargain signal
Prices sometimes fall because the business is weakening. A low P/E may reflect real problems that later show up in lower earnings.
What's the bottom line?
The P/E ratio compresses price and profit into one number: how many dollars you pay for each dollar of yearly earnings. It is useful for comparing similar companies or a company with its own past, but it depends on which earnings are used and says nothing on its own about quality or risk. To see the earnings figure at its source, read how to read financial statements, and for how style indexes use ratios like P/E, see growth vs value stocks.
Frequently asked questions
What does a P/E of 25 mean?
It means the share price is 25 times the company's earnings per share. Investors are paying $25 for each $1 of yearly profit. Whether that is high depends on the industry and the company's growth.
Can a P/E ratio be negative?
If a company loses money, its EPS is negative and the calculated P/E is negative. Most data sites show it as not meaningful (often "N/A") because the ratio cannot be interpreted in the usual way.
Is a lower P/E always better?
No. A low P/E can reflect a slow-growing business, a temporary profit spike, or problems investors expect to hit future earnings. It is a prompt to look closer, not a signal to buy.
Where do I find a company's EPS?
Public companies report EPS in the income statement of their Form 10-K and 10-Q filings, which are free on the SEC's EDGAR website. Financial data sites also publish it, but check which figure they use.
Sources
Grade A = primary source (regulator, government agency, official rulebook or the index provider's own documents). Numbers in brackets in the text point here.
- U.S. SEC — Investor.gov. Price-earnings (P/E) Ratio (glossary) (2026). Accessed 2026-10-03.A
- FINRA. Financial Performance Metrics Every Investor Should Know (2026). Accessed 2026-10-03.A
- U.S. SEC — Investor.gov. Earnings Per Share (glossary) (2026). Accessed 2026-10-03.A
- FINRA. Evaluating Stocks (2026). Accessed 2026-10-03.A
- Bogleheads wiki. P/E (2026). Accessed 2026-10-03.B
- FINRA. Value Investing (2026). Accessed 2026-10-03.A
This page is general education, not personal financial, tax or legal advice. Figures in worked examples are hypothetical and calculated before taxes and fees unless stated. Rules and limits change; check the linked primary sources for the current version. How we check every page.
