There is no single good P/E ratio. As a rough guide, a P/E between about 15 and 25 is ordinary for an established company, below 15 is low and above 25 is high. But a "good" P/E depends on how fast the company is growing, how reliable its profits are, and which industry it belongs to. A P/E only means something when you compare it with the right things.
What the P/E ratio measures
The price-to-earnings ratio tells you how much investors are paying for each unit of a company's profit. In words: take the share price and divide it by the earnings per share. Earnings per share, or EPS, is the company's net profit divided by the number of shares outstanding.
P/E = Share price ÷ Earnings per share
Example (invented numbers): a company's shares trade at 60. Over the last twelve months it earned 4 per share. Its P/E is 60 ÷ 4 = 15. Put differently, if profits stayed exactly flat, it would take 15 years of earnings to add up to what you paid for the share.
That last sentence is the most useful way to think about P/E. It is a payback period in disguise. A P/E of 10 implies a ten-year payback, a P/E of 40 implies forty years, unless profits grow. Growth is what makes a high P/E reasonable, and its absence is what makes a low P/E cheap for a reason.
What a good P/E looks like
Over long stretches of history, the broad US stock market has tended to trade somewhere in the mid-teens to low twenties. That gives a loose anchor, nothing more. Within that, P/E ratios vary widely by type of business:
Slow-growing, mature businesses such as utilities, tobacco and many banks often trade between about 8 and 15. Their profits are steady but rarely expand quickly.
Steady compounders, companies with strong brands and dependable growth, frequently sit between 20 and 30. Investors pay up for reliability.
Fast-growing companies can trade at 40, 60 or more, because the market expects today's earnings to be a small fraction of future earnings.
Cyclical businesses such as carmakers, steelmakers and airlines behave oddly, which is covered below.
So the useful question is not "is this P/E low?" but "is this P/E low for this kind of business, growing at this rate?" Three comparisons answer it best:
Against the company's own history. If a business has traded between 18 and 25 for a decade and now sits at 14, something has changed. Find out what.
Against close competitors. A software company at 30 may be cheap next to peers at 45. A bank at 14 may be expensive next to peers at 9.
Against its growth rate. A P/E of 30 for a company growing earnings at 20% a year can be better value than a P/E of 12 for one whose earnings are shrinking.
Why a low P/E can be a trap
A low P/E is the most common reason people buy a stock that then keeps falling. The market is not always right, but it is rarely random either. Prices are often low because investors expect profits to fall. When they do, the "cheap" P/E turns out to have been calculated on earnings that no longer exist.
Example (invented numbers): a retailer earns 5 per share and trades at 30, a P/E of 6. It looks like a bargain. The next year, competition squeezes its profits to 2 per share. At the same price of 30, its P/E is now 15. Nothing about the share price changed. The bargain was never there.
This is called a value trap: a stock that looks cheap on a single measure but is cheap because the business is weakening. A low P/E is a reason to investigate, never a reason on its own to buy.
What the P/E ratio doesn't tell you
The P/E is popular because it is one number. That is also its weakness. It leaves out a great deal:
Debt. Two companies can share a P/E of 15 while one has no debt and the other owes several years of profit to lenders. The P/E treats them as equally priced. They are not.
Quality of earnings. Reported profit can include one-off gains, such as selling a building, or accounting choices that flatter the figure. Free cash flow, the cash a business actually keeps, is often a more honest check.
Cyclical distortion. For cyclical companies, the P/E often looks lowest at the top of the cycle, when profits are at a peak and about to fall, and highest at the bottom, when profits are depressed and about to recover. Reading it the normal way can lead you to buy at exactly the wrong time.
Losses. A company that loses money has no meaningful P/E at all. A company with tiny profits can show a P/E of 300 that tells you very little.
Reinvestment. A business that spends heavily on growth today may report low profits and a high P/E, even if those investments will pay off well. The P/E captures this year, not the next ten.
Banks and insurers deserve a specific mention. Their earnings swing with credit losses and investment results, and many analysts prefer price-to-book for them. A low P/E on a bank can simply reflect the market pricing in future loan losses.
Trailing P/E versus forward P/E
You will see two versions. The trailing P/E uses actual earnings from the last twelve months, often labelled TTM. The forward P/E uses analysts' estimates of next year's earnings. Trailing is based on facts but looks backwards. Forward looks ahead but rests on forecasts that are often too optimistic. When the two differ sharply, ask why analysts expect earnings to change so much, and how confident you are that they are right.
How to use the P/E ratio
Treat the P/E as the first filter, not the verdict. A sensible order of work looks like this:
Use the P/E to notice when a company is priced unusually high or low against its own history and its peers.
Check whether earnings are real and repeatable: look at free cash flow, profit margins and several years of results, not one.
Check the balance sheet, so debt does not hide behind a low P/E.
Look at growth, because growth is what justifies paying more.
Finally, estimate what the business is worth and compare that with the price, leaving yourself a margin of safety.
Our company library puts the P/E next to return on capital, debt, growth and free cash flow for each company, so you can see the number in context rather than on its own.
FAQ
Is a P/E ratio of 20 good?
It can be. For a steady business growing earnings at 8–12% a year, a P/E around 20 is ordinary. For a slow-growing utility it would be expensive, and for a fast-growing software company it would be low. Compare it with the company's history, its peers and its growth rate.
Is a negative P/E ratio bad?
A negative P/E means the company lost money over the period, so the ratio has no useful meaning. It is not automatically bad, since young companies often lose money while they grow, but you will need other measures, such as revenue growth and cash position, to judge it.
Should I only buy stocks with a low P/E?
No. Some of the best long-term investments rarely looked cheap on P/E, because their earnings kept growing. Some of the worst looked cheap the whole way down. A low P/E deserves a closer look, not an automatic purchase.
The short version
A good P/E is one that is reasonable for the business you are looking at: its growth, its reliability and its industry. The ratio is a fast way to spot something worth investigating and a poor way to make a final decision. Read it alongside debt, cash flow and growth, and it becomes genuinely useful.
This article is for educational purposes only and is not investment advice.
