P/E Ratio Explained: What Is a Good Price-to-Earnings Ratio?

The P/E ratio, or price-to-earnings ratio, tells you how many dollars investors are paying for each $1 of a company’s annual profit. You calculate it by dividing the share price by earnings per share: a $60 stock that earned $3 per share over the past year trades at a P/E of 20.

With the P/E ratio explained in one sentence, the harder question is what counts as “good.” There is no single magic number. A P/E of 12 can be expensive for a shrinking business, and a P/E of 35 can be reasonable for a company growing profits 25% a year. The ratio only becomes useful when you compare it with something: the same company’s history, its industry, the whole market, and its expected growth.

This guide covers the formula, trailing vs forward P/E, a worked example, what a “good” P/E looks like by sector and against the S&P 500’s long-run record, plus three related measures (the PEG ratio, earnings yield and the CAPE ratio) and the traps that make a cheap-looking P/E misleading.

What Is the P/E Ratio?

The price-to-earnings ratio is the most widely quoted valuation multiple in the stock market. A valuation multiple compares a company’s price with some measure of its business, so you can judge whether the price looks high or low relative to what you get.

P/E uses profit as that measure. Think of it as a payback period in a very rough sense: at a P/E of 20, if earnings stayed flat forever and every dollar were paid out to you, it would take about 20 years of profits to “earn back” the price. Higher P/E means investors are paying more for each dollar of current profit, usually because they expect that profit to grow.

That expectation is the key. A high P/E is not a verdict that a stock is overpriced, and a low P/E is not proof of a bargain. The ratio describes what the market is currently assuming. Your job is to decide whether those assumptions look reasonable. If you are new to how shares are priced, start with our guide to how the stock market works.

The P/E Ratio Formula

The standard P/E ratio formula is:

P/E ratio = Share price ÷ Earnings per share (EPS)

Earnings per share (EPS) is a company’s net income, minus any preferred dividends, divided by the number of common shares outstanding. Most data providers use diluted EPS, which counts shares that could be created from stock options and convertible securities, so the figure is not flattered by ignoring them.

You can get the same answer at the whole-company level:

P/E ratio = Market capitalization ÷ Net income

Here market capitalization is the share price multiplied by the number of shares. A company worth $50 billion that earned $2.5 billion last year has a P/E of 20, exactly as if you had done the per-share math.

Two practical points. First, the “E” is normally the last four quarters of earnings, not a single quarter. Second, check which earnings figure is being used. Reported earnings follow accounting standards (GAAP in the US). “Adjusted” or “operating” earnings, which companies and analysts often prefer, strip out items management considers unusual, and they usually produce a lower, friendlier P/E.

Trailing P/E vs Forward P/E

When you see a P/E quoted, it is one of two versions, and the gap between them can be large.

• Trailing P/E (also written TTM, for trailing twelve months) uses the actual EPS reported over the past four quarters. It is based on real numbers, but it looks backward.
• Forward P/E uses analysts’ consensus forecast of EPS for the next 12 months or the next fiscal year. It looks ahead, but it depends on forecasts that are often too optimistic and get revised.

If a stock’s forward P/E is much lower than its trailing P/E, analysts expect earnings to rise sharply. If forward is higher than trailing, they expect earnings to fall. Either way, the difference tells you how much of the valuation rests on a forecast rather than on results already in the bank.

Worked example: P/E ratio explained with numbers

This is the pattern you will see again and again: a P/E comparison is really a comparison of growth expectations.

What Is a Good P/E Ratio?

A “good” P/E is one that is reasonable relative to the company’s growth, risk and profitability. Three reference points help.

Compared with the S&P 500’s history

Using Robert Shiller’s long-run data, multpl.com puts the mean trailing P/E of the S&P 500 (and its predecessor indexes) since 1871 at about 16.2, with a median of about 15.1. As of October 22, 2026, the index’s trailing P/E stood at about 26 on the same site. You can check the live figure there, because it changes every trading day.

So a rule of thumb many investors use is that the market has historically traded around 15 to 17 times earnings, and the US market has spent much of the past decade well above that. The extremes are instructive too. The lowest reading in that series, about 5.3, came in December 1917. The highest, about 124, came in May 2009, not because stocks were wildly loved but because earnings had collapsed during the financial crisis. That is a reminder that P/E can be high because “P” is high or because “E” is temporarily tiny.

Compared with its sector

Industries trade at very different multiples because they grow at different speeds and carry different risks. Professor Aswath Damodaran of NYU Stern publishes P/E data by industry for US companies. In his data as of January 2026, forward P/Es looked roughly like this:

These numbers move every year, so treat them as an illustration of the spread, not as targets. The lesson is that a P/E of 25 might be cheap for a software company and expensive for a bank.

Compared with its own history and growth

The most useful comparison is often a company against itself. If a business has traded between 15 and 22 times earnings for a decade and now sits at 30, ask what changed. Maybe growth has genuinely accelerated. Maybe the market is simply more excited. Then compare the P/E with the growth rate, which brings us to the PEG ratio.

P/E vs PEG Ratio

The PEG ratio (price/earnings-to-growth) adjusts P/E for expected earnings growth:

PEG ratio = P/E ratio ÷ Annual EPS growth rate (as a whole number)

Investor Peter Lynch popularized the idea in his 1989 book One Up on Wall Street, arguing that a fairly priced company’s P/E roughly equals its growth rate. On that view, a PEG around 1 is “fair,” below 1 looks cheap for the growth on offer, and well above 1 looks expensive.

PEG has real limits. The growth figure is a forecast, usually for three to five years, and long-range forecasts are unreliable. It ignores dividends, so it understates the value of slow-growing, high-payout companies. And it says nothing about risk: a 30% grower with a fragile balance sheet deserves a lower multiple than a 30% grower with net cash.

Earnings Yield and the CAPE Ratio

Earnings yield

Earnings yield is the P/E ratio flipped upside down: EPS ÷ price, shown as a percentage. A P/E of 20 equals an earnings yield of 5%; a P/E of 25 equals 4%; a P/E of 10 equals 10%.

The advantage is that you can line it up against other yields, such as a savings rate or a government bond yield. When bond yields are high, stocks at a 4% earnings yield face tougher competition than when bond yields are near zero, which is one reason market P/Es tend to fall when interest rates rise. The comparison is loose, though: bond coupons are fixed, while company earnings can grow, shrink or vanish. It also handles losses gracefully. A company with negative earnings simply has a negative earnings yield, rather than a meaningless P/E.

The CAPE ratio (Shiller P/E)

The cyclically adjusted price-to-earnings ratio (CAPE) divides the price by the average of the past 10 years of earnings, with both adjusted for inflation. John Campbell and Robert Shiller introduced the approach in academic work published in 1988, and Shiller later made it famous. Averaging a decade of profits smooths out recessions and boom years, so CAPE is not distorted the way the single-year P/E was in 2009.

According to multpl.com, the S&P 500’s CAPE has averaged about 17.4 since 1871, peaked at about 44.2 in December 1999, and stood at about 40.6 as of October 22, 2026. Research has found that high starting CAPE readings have tended to be followed by lower returns over the next 10 to 20 years. It is a poor timing tool, though. CAPE can stay well above average for many years, and changes in accounting rules and in the mix of companies in the index make long-run comparisons imperfect.

P/E Ratio Pitfalls to Avoid

The P/E ratio is simple, which makes it easy to misuse. These are the most common traps.

• Negative earnings. When a company loses money, P/E is not meaningful, and most sites show “N/A” or a dash. Many young growth companies and turnaround stories fall into this bucket. You will need other measures, such as price-to-sales or cash flow, to value them.
• One-off items. A big asset sale, legal settlement, write-down or tax benefit can swing reported earnings for a year. Suppose a stock trades at $50 and reported EPS is $5, a P/E of 10. If $2 of that EPS came from selling a division, underlying EPS is $3 and the real P/E is $50 ÷ $3 = 16.7. Read the earnings release before trusting the headline number.
• Cyclical companies. Steelmakers, carmakers, miners, chip producers and airlines see profits swing with the economy. Their P/E often looks lowest at the top of the cycle, when earnings peak, and highest near the bottom. A steelmaker at $60 earning $10 a share at the peak trades at a P/E of 6; if earnings fall to $1 and the price drops to $40, the P/E jumps to 40. Buying cyclicals because their P/E looks low is a classic mistake.
• Buybacks and leverage. Share buybacks shrink the share count and lift EPS, and borrowed money can boost returns. Two companies on the same P/E can carry very different debt loads. Check the balance sheet.
• Apples-to-oranges comparisons. Comparing a bank’s P/E with a software company’s, or a US stock’s with one listed in a market with different accounting rules and growth prospects, tells you little.
• Value traps. A stock can look cheap on P/E because its earnings are about to fall. A low multiple sometimes means the market sees trouble you have not spotted yet.

P/E vs Other Valuation Ratios

No single ratio is enough. Professional analysts look at several, because each one highlights something the others miss.

Enterprise value (EV) is market capitalization plus debt minus cash, roughly the price to buy the whole business including its borrowings. For dividend-paying companies, our guide to dividend stocks for beginners explains yield and payout ratios in more detail.

How to Use the P/E Ratio in Practice

A simple routine keeps P/E in its proper place as a starting point for research rather than a buy or sell signal.

1. Check which P/E you are looking at. Trailing or forward, reported or adjusted earnings.
2. Compare with peers. Line the company up against three to five direct competitors in the same industry.
3. Compare with its own history. Is today’s P/E near the top, middle or bottom of its 5- to 10-year range, and why?
4. Bring in growth. Calculate a PEG ratio, and ask how confident you are in the growth estimate.
5. Look under the hood. Scan for one-off items, debt, buybacks and whether the business is cyclical.
6. Cross-check. Use at least one other ratio, such as price-to-sales, EV/EBITDA or free cash flow yield.

P/E is also central to the debate between growth vs value stocks: value investors hunt for low multiples, while growth investors accept high ones in exchange for faster earnings growth. If you prefer not to analyze individual companies at all, a broad S&P 500 index fund lets you own the whole market at its average multiple.

Bottom Line

The P/E ratio divides share price by earnings per share and tells you what the market is paying for each dollar of profit. There is no universally good number: judge it against the company’s industry, its own history, its expected growth (via the PEG ratio) and the market’s long-run average of roughly 15 to 17. Watch for losses, one-off items and cyclical earnings, and always pair P/E with other measures. For a broader foundation, read our guide on how to invest in stocks or browse more stock market guides.

Sources

• multpl – S&P 500 PE Ratio (historical and current)
• multpl – Shiller PE Ratio (CAPE) for the S&P 500
• Robert Shiller, Yale University – Online Data
• NBER – Campbell and Shiller, Stock Prices, Earnings and Expected Dividends
• NYU Stern, Aswath Damodaran – Price Earnings Ratios by Industry
• Investor.gov (US SEC) – Stocks FAQs