What Is the P/E Ratio? Formula and Examples

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The price-to-earnings (P/E) ratio is a company’s share price divided by its earnings per share (EPS). It tells you how many dollars investors are paying for each $1 of the company’s annual profit. A stock trading at $40 with EPS of $2 has a P/E of 20: buyers are paying $20 for every $1 of earnings. Because it scales price to profit, the P/E ratio lets you compare the valuation of companies with very different share prices, and compare one company’s valuation today with its own past.

The P/E ratio is also called the price multiple, the earnings multiple, the price-earnings ratio or, in some markets and trading platforms, the PER. All of these names describe the same calculation.

What the P/E Ratio Measures

A share of stock is a claim on a slice of a company’s future profits. The P/E ratio connects the price of that claim to the profit the company currently produces (or is expected to produce) for each share. It does not measure whether a company is good, safe or growing. It measures how the market prices its earnings.

That makes the ratio a measure of expectations. Two companies can each earn $1 per share and trade at very different prices. If one trades at $10 and the other at $40, the market is paying four times as much for the second company’s earnings. Investors may expect those earnings to grow faster, consider them more reliable, or simply be more enthusiastic about the business. The P/E captures the result in one number, but not which judgment drives it.

This is why the P/E ratio is used in three main ways:

1. Against peers. Comparing a company’s P/E with that of competitors in the same industry shows whether the market values it at a premium or a discount.
2. Against its own history. A company trading at 12 times earnings when it has historically traded between 18 and 25 times is priced differently than usual, and the analyst’s job is to find out why.
3. Against the market. Comparing a stock’s P/E to a broad index such as the S&P 500 shows whether investors are paying more or less than average for its earnings.

P/E Ratio Formula

The standard P/E ratio formula is:

P/E ratio = Market value per share ÷ Earnings per share (EPS)

The numerator is the current share price. The denominator is earnings per share: the company’s net income attributable to common shareholders, divided by the number of shares outstanding.

Multiplying both sides by the number of shares gives the company-level version:

P/E ratio = Market capitalization ÷ Net income

Both versions give the same answer when the share count is consistent; the per-share version is more commonly quoted.

How to Calculate P/E Step by Step

1. Find the current share price. This is the price at which the stock last traded.
2. Choose the EPS figure. Decide between trailing and forward EPS, and between basic and diluted EPS (explained below).
3. Divide the price by EPS. The result is expressed as a number or a multiple, such as 20 or 20x.

Choosing the Right EPS Input

The share price is a single observable figure. EPS is not. The same company can have several legitimate EPS figures, and the P/E ratio you calculate depends on which one you pick.

• Basic vs. diluted EPS. Basic EPS divides earnings by the shares currently outstanding. Diluted EPS adds shares that could be created if stock options, warrants, convertible bonds and similar securities were exercised or converted. Diluted EPS is lower (or equal), so a P/E based on diluted EPS is higher (or equal). Diluted EPS is the more conservative choice when comparing companies.
• Reported vs. adjusted EPS. Reported (GAAP) earnings follow accounting standards. Many companies also publish adjusted earnings that exclude items such as restructuring costs, asset write-downs or gains from selling a business. A P/E based on adjusted EPS can look quite different from one based on reported EPS.
• Time period. Trailing EPS covers the last four reported quarters. Forward EPS covers estimates for the coming year. A third, less common version combines the last two reported quarters with estimates for the next two.

When you compare P/E ratios across companies or across time, use the same type of EPS for each. A trailing GAAP P/E for one company and a forward adjusted P/E for another are not comparable numbers.

Trailing P/E vs. Forward P/E

The two most widely used versions of the P/E ratio differ only in the earnings figure in the denominator, but they answer different questions.

Trailing P/E

Trailing P/E divides the current share price by the total EPS for the previous 12 months, often labeled TTM (trailing twelve months). It is the most commonly quoted version because it relies on earnings the company has actually reported, which are audited or at least reviewed, rather than on forecasts.

Its weakness is that it looks backward, while investors buy stocks for future earnings. It also mixes timeframes: the price updates every trading session, while earnings update once a quarter. If something significant happens between reports, such as a lost contract or a new product, the price may react immediately while trailing EPS still reflects the old situation, so the P/E moves only because the price moved.

Forward P/E

Forward P/E (also called leading P/E or estimated price-to-earnings) divides the current share price by expected EPS for the next 12 months. Those estimates come from company guidance, from analysts who cover the stock, or from a consensus average of analyst forecasts.

Forward P/E lines the price up with the earnings investors are actually trying to buy, but its denominator is an estimate. Companies may guide conservatively so that results beat expectations. Analysts’ estimates may differ from guidance and from each other, so two data sources can show different forward P/E ratios for the same stock on the same day.

Reading the Two Together

Comparing trailing and forward P/E shows what the market’s estimates imply about the direction of earnings:

• Forward P/E lower than trailing P/E: estimated future EPS is higher than past EPS, so analysts expect earnings to grow.
• Forward P/E higher than trailing P/E: estimated future EPS is lower than past EPS, so analysts expect earnings to fall.

Examples of the P/E Ratio

The following examples use hypothetical companies and figures to show the mechanics. They are not data on real stocks.

Basic Calculation

Hypothetical example. Company A’s shares trade at $50. Over the last four quarters, it reported diluted EPS of $2.50.

Trailing P/E = $50 ÷ $2.50 = 20

Investors are paying $20 for every $1 of Company A’s past-year earnings.

The same answer comes from the company-level formula. Suppose Company A has 200 million shares outstanding (on a diluted basis). Its market capitalization is 200 million × $50 = $10 billion, and its net income is 200 million × $2.50 = $500 million. $10 billion ÷ $500 million = 20.

Forward P/E for the Same Company

Hypothetical example. Analysts expect Company A to earn $3.125 per share over the next 12 months.

Forward P/E = $50 ÷ $3.125 = 16

The forward P/E (16) is below the trailing P/E (20), which tells you analysts expect earnings to grow by 25% ($2.50 to $3.125). If those estimates prove too optimistic, the “real” forward multiple will turn out higher than 16.

Comparing Two Companies

Hypothetical example. Two companies in the same industry:

• Company X: share price $80, trailing diluted EPS $4.00, P/E = 20
• Company Y: share price $45, trailing diluted EPS $3.00, P/E = 15

Company X’s share price is higher in dollars, but that alone says nothing about value. The P/E ratio shows that the market pays $20 for each $1 of X’s earnings and $15 for each $1 of Y’s. X trades at a premium.

That premium has more than one possible explanation: X may be overvalued, or the market may expect its earnings to grow faster or be more stable than Y’s. Separating those requires looking at growth rates (see the PEG ratio below), balance sheets, competitive position and each company’s earnings history.

How the Ratio Moves

Because the P/E is a fraction, it changes when either the price or the earnings change. Starting from Company A’s P/E of 20 ($50 ÷ $2.50):

• Price falls, earnings unchanged. The stock drops to $40. P/E = $40 ÷ $2.50 = 16. The stock is cheaper per dollar of earnings.
• Earnings rise, price unchanged. EPS grows to $3.33. P/E = $50 ÷ $3.33 ≈ 15. The stock became cheaper on this measure without the price moving.
• Earnings fall, price unchanged. EPS drops to $1.25. P/E = $50 ÷ $1.25 = 40. The stock now looks expensive, even though the price never moved.

The last case matters for cyclical businesses such as automakers, steelmakers or commodity producers, whose profits swing with the economy. At the bottom of a cycle, depressed earnings can produce a very high P/E even when the share price is low. Near the top of a cycle, peak earnings can make the P/E look low just before profits decline. For these companies, a single year’s P/E can point in the wrong direction, which is one reason long-term averages of earnings (covered below) were developed.

Share buybacks also move the ratio. When a company repurchases its own shares, the same net income is divided among fewer shares, so EPS rises. If the price stays the same, the P/E falls, even though the business’s total profit has not changed.

How to Interpret a P/E Ratio

A P/E of 25 means paying $25 per $1 of earnings; a P/E of 10 means paying $10. Reading the number requires asking why the market is willing to pay that amount.

What a High P/E Can Mean

A high P/E means the price is high relative to current earnings. Possible reasons include:

• Expected growth. Investors expect earnings to rise substantially, so today’s price reflects profits that do not exist yet.
• Perceived quality or stability. Investors may pay more for earnings they see as reliable, for example from a company with recurring revenue or a strong market position.
• Temporarily depressed earnings. A one-time charge or a cyclical downturn has shrunk the denominator.
• Overvaluation. The price has simply run ahead of what the business is likely to earn.

A high P/E is not automatically a warning, and it is not automatically a sign of a great company. It means more of the stock’s value depends on the future.

What a Low P/E Can Mean

A low P/E means the price is low relative to current earnings. Possible reasons include:

• Undervaluation. The market may be overlooking the company.
• Expected decline. Investors may believe earnings will fall, because the industry is shrinking, the business model is weakening, or a major customer is at risk. In that case the bargain is an illusion: today’s earnings overstate what future earnings will be.
• Temporarily inflated earnings. A one-time gain, such as the sale of a division, can boost EPS for a year and make the P/E look lower than the business’s normal earnings would justify.
• Higher risk. Heavy debt, legal exposure or governance concerns can lead investors to pay less per dollar of profit.

When the P/E Is N/A or Negative

A P/E of N/A means the ratio is not available. This happens when:

• The company has negative earnings (a loss).
• The company has zero earnings, which would require dividing by zero.
• The company is newly listed, for example after an initial public offering (IPO), and has not yet reported a full year of earnings as a public company.

Dividing a positive price by a negative EPS gives a negative P/E, but the result has no useful meaning: a P/E of negative 20 does not make a stock “cheaper” than one at 10. Some analysts show a negative P/E, some assign zero, and many treat the P/E as not existing until the company is profitable. For unprofitable companies, the price-to-sales ratio or the earnings yield is more practical.

What Is a Good P/E Ratio?

There is no single good P/E ratio. A P/E that is ordinary for a software company may be unusual for a utility. Industries differ in growth, capital needs, cyclicality and perceived risk, and those differences show up in typical P/E levels.

A high P/E is less of a concern when the whole sector trades at high multiples, and more of a question when it stands far above similar companies. Compare against those peers using the same EPS type, and against the company’s own range across a full business cycle.

Whether a lower P/E is “better” depends on what you are paying for. A lower P/E means a lower price per dollar of current earnings, which is why value investors often favor low-P/E stocks. But a company with a P/E of 30 that doubles its earnings in a few years may turn out cheaper than one with a P/E of 8 whose earnings halve. The P/E is a starting point for that judgment, not the judgment itself.

The Market’s P/E and the Cyclically Adjusted P/E

The P/E ratio can be calculated for an entire stock index by comparing the index’s level to the combined earnings of its member companies. Investors track the P/E of the S&P 500, for example, to gauge whether U.S. large-cap stocks as a group are priced high or low relative to their earnings.

The market’s P/E has varied widely. Using S&P 500 data going back to 1927, the index’s P/E fell to roughly 6 in mid-1949 and reached about 122 in mid-2009. The 2009 peak shows the denominator problem described above: after the financial crisis, corporate earnings collapsed, so the ratio spiked even though stock prices had fallen sharply. The market was not extraordinarily expensive; its earnings were temporarily crushed.

To smooth out such distortions, analysts use long-term averages of earnings:

• P/E 10, also known as the cyclically adjusted price-to-earnings ratio (CAPE) or Shiller P/E after economist Robert Shiller, who popularized it, divides price by the average of the past 10 years of earnings, adjusted for inflation.
• P/E 30 applies the same idea over 30 years.

Because these measures average earnings across several business cycles, a single boom or bust year has less influence. They are used mainly to judge whole markets over long periods rather than to pick individual stocks. The inflation adjustment matters because nominal earnings from a decade ago are not comparable to today’s without it.

P/E vs. Earnings Yield

The earnings yield is the P/E ratio turned upside down:

Earnings yield = EPS ÷ Share price, expressed as a percentage

Hypothetical example. Stock A trades at $10 with trailing EPS of $0.50. Its P/E is 20 ($10 ÷ $0.50) and its earnings yield is 5% ($0.50 ÷ $10). Stock B trades at $20 with trailing EPS of $2. Its P/E is 10 and its earnings yield is 10%.

The two measures carry the same information; the earnings yield frames it as a rate of return. For every $100 invested in Stock A, the company earns $5 a year, which makes comparison with bonds and other yielding assets easier. That is not a cash return to shareholders, because the company may retain much of its earnings rather than pay dividends.

The earnings yield also handles losses: a company with negative EPS has an N/A P/E but a negative earnings yield, which can still be ranked against other companies, including early-stage firms that are not yet profitable.

P/E vs. PEG Ratio

A P/E ratio, even a forward one, does not tell you whether the multiple is reasonable for the company’s growth rate. A P/E of 30 might be modest for a company growing earnings at 40% a year and steep for one growing at 3%. The price/earnings-to-growth (PEG) ratio addresses this:

PEG ratio = P/E ratio ÷ Annual EPS growth rate (growth expressed as a whole number, so 25% growth is entered as 25)

PEG ratios can be “trailing,” using historical growth rates, or “forward,” using projected growth.

Hypothetical example. Returning to the two companies above:

• Company X: P/E 20, expected annual EPS growth 25%. PEG = 20 ÷ 25 = 0.8
• Company Y: P/E 15, expected annual EPS growth 5%. PEG = 15 ÷ 5 = 3.0

On P/E alone, Y looked cheaper. Once growth is included, X looks cheaper relative to its expected growth. A common rule of thumb treats a PEG below 1 as a sign of possible undervaluation and above 1 as a sign of possible overvaluation, although typical growth rates differ by sector and the rule is a convention rather than a law.

The PEG ratio inherits the weaknesses of its inputs. The growth rate is usually an estimate, and small changes in that estimate move the result a lot. It also breaks down for companies with negative or very low growth.

Absolute vs. Relative P/E

Analysts sometimes distinguish between the P/E itself and the P/E measured against a benchmark.

Absolute P/E

The absolute P/E is the ordinary ratio for the current period, using trailing, forward or blended EPS.

Hypothetical example. A stock trades at $100 with trailing EPS of $2. Its absolute P/E is $100 ÷ $2 = 50.

Relative P/E

The relative P/E compares the absolute P/E with a benchmark, usually the company’s own P/E range over a past period such as 10 years, or an index P/E.

Relative P/E = Current P/E ÷ Benchmark P/E × 100%

Hypothetical example. A company’s current P/E is 18. Over the past 10 years, its P/E ranged from a low of 12 to a high of 30.

• Against the high: 18 ÷ 30 = 60%. The stock trades at 60% of its peak multiple.
• Against the low: 18 ÷ 12 = 150%. The stock trades at one and a half times its lowest multiple.

A relative P/E below 100% means the current P/E is below the benchmark; at 100% or more, it has reached or exceeded it. Against the high, it shows how much room remains before the historical peak valuation; against the low, how far the stock sits from its historical floor.

Limitations of the P/E Ratio

It works poorly across industries. Valuation and growth vary widely between industries, so comparing a retailer’s P/E with an oil and gas driller’s says little about which is the better investment. P/E comparisons are useful mainly within a sector.

Earnings are an accounting figure. Net income depends on choices about depreciation, revenue recognition, inventory valuation, one-time items and more. Two companies with identical cash generation can report different EPS. Earnings can also include gains or charges that will not recur, distorting a single year’s ratio.

Earnings come from the company. The price is set by the market, but earnings are reported by management, so investors must trust them. Because it is hard to manipulate results while keeping all financial metrics consistent, checking the P/E alongside cash flow and balance sheet measures helps reduce this risk.

It ignores debt. A company’s debt affects both its earnings (through interest costs) and its share price (through risk). Leverage can therefore skew P/E comparisons. Of two otherwise similar companies, the one carrying more debt may trade at a lower P/E because investors see it as riskier, yet if the business is sound, borrowing may have helped it produce higher earnings.

It reflects one point in time. The price changes every trading session and earnings every quarter, so the ratio is a snapshot of both; tracking how earnings change year over year adds context.

Alternatives to the P/E Ratio

Where the P/E ratio struggles, other valuation multiples can fill in. Each puts a different figure in the denominator.

Price-to-book (P/B) ratio. Compares market value to book value, the net assets on the balance sheet (assets minus liabilities, or shareholders’ equity). It suits businesses with substantial tangible or financial assets. A low P/B may indicate undervaluation, or assets the market doubts are worth their book value.

Price-to-sales (P/S) ratio. Compares market value (or share price) to revenue. Because revenue is positive even when a company is losing money, the P/S ratio works for companies that are not yet profitable or have volatile earnings, such as early-stage technology firms. It shows how much investors pay per dollar of sales, but not whether those sales will ever turn into profit.

Enterprise value to EBITDA (EV/EBITDA). Enterprise value adds debt to market capitalization and subtracts cash, measuring the whole business rather than just the equity. EBITDA is earnings before interest, taxes, depreciation and amortization. Because it accounts for debt and cash, EV/EBITDA compares companies with different capital structures better than the P/E, and it is often used for capital-intensive industries such as telecommunications and utilities.

In practice, analysts look at several of these measures together. If a stock looks cheap on P/E but expensive on EV/EBITDA, the difference often points to debt, and that is worth investigating before drawing a conclusion.

P/E Ratios for Banks

Banks show why the P/E needs industry context. A bank’s earnings depend on the gap between loan and deposit rates, which moves with interest rates, and on provisions for loan losses, so reported earnings can shift sharply from year to year. Because a bank’s balance sheet consists largely of financial assets carried near their stated values, analysts commonly look at price-to-book alongside the P/E. EV/EBITDA is rarely applied to banks, because debt and interest are part of the core business rather than a financing choice.

FAQs

The Bottom Line

The P/E ratio matters to investors who want a quick read on how the market prices a company's earnings. It works best against similar companies in the same industry, or against the company's own history, using the same type of EPS each time. A high or low number needs explanation, so check growth, debt and cash flow, and use measures such as price-to-sales or EV/EBITDA where the P/E falls short.