Suppose two companies each trade at $100 per share. Are they equally expensive? That question cannot be answered from the share price alone. One company might earn $10 per share each year. Another might earn $1. The first stock would be trading at ten times annual earnings. The second would trade at one hundred times annual earnings.
That relationship is captured by the price-to-earnings ratio, usually written as P/E.
FINRA defines the P/E ratio as a company's current stock price divided by its earnings per share. The ratio expresses how much investors are currently paying for each dollar of company earnings.
The formula is: P/E ratio = share price divided by earnings per share.
If a company's stock trades at $60 and the company earns $3 per share, its P/E ratio is 20.
Investors are therefore paying $20 in stock-market value for each $1 of current annual earnings per share.
Why would investors pay a high P/E?
Usually because they expect something about the future.
A company growing earnings quickly may deserve a higher valuation than a mature company whose earnings are barely increasing.
Imagine two businesses each earn $2 per share.
Company A is expected to remain near $2 for several years.
Company B has been expanding rapidly and investors believe its earnings could reach $6 per share.
Investors may be willing to pay considerably more for Company B today because they are valuing the possibility of greater future earnings.
This explains why a high P/E ratio does not automatically mean a stock is overpriced.
It means the market is placing a relatively high valuation on the company's current earnings.
Whether that valuation is justified depends on what happens next.
A low P/E can be a warning as easily as an opportunity
Beginners sometimes search for the lowest P/E ratio available and assume they have found a bargain.
Markets are usually more complicated.
A company's P/E may be low because investors expect its profits to decline. The company could operate in an industry facing structural problems. It may carry significant debt or have unusually volatile earnings.
If earnings fall sharply next year, today's apparently cheap valuation may prove misleading.
This is why valuation ratios require context.
Comparing a rapidly growing software company with a regulated utility using only P/E ratios may reveal little because the two businesses can have completely different growth rates, risk profiles, capital requirements, and economics.
Comparisons are often more informative among reasonably similar companies.
Trailing P/E and forward P/E are different
Another detail matters when reading financial websites.
A trailing P/E usually relies on earnings already reported over the prior twelve months.
A forward P/E generally uses analysts' estimates of future earnings.
The forward version therefore depends on forecasts.
If expected earnings never materialize, the ratio investors thought they were paying can change dramatically.
Suppose a stock trades at $100 and analysts expect $5 of earnings next year. Its forward P/E is 20.
If the company ultimately earns only $2.50, the same $100 stock price would represent 40 times those earnings.
The valuation did not become more expensive because the stock price rose. The earnings assumption deteriorated.
What if the company has no earnings?
A conventional P/E ratio becomes far less useful when a company is losing money.
Dividing the share price by negative earnings does not produce an economically meaningful valuation multiple in the usual sense.
Investors may then examine other measures, such as revenue, cash flow, unit economics, or industry-specific metrics.
Those alternatives carry their own limitations.
There is no ratio capable of replacing an understanding of the business itself.
Why P/E is still useful
The P/E ratio survives because it compresses a meaningful relationship into one number.
It tells an investor how much the market is currently valuing a company's earnings.
That can make comparisons easier and help reveal the assumptions embedded in a stock price.
A P/E of 50, for example, does not announce whether a stock should be bought or sold. It tells the investor that the market is assigning a rich valuation relative to current earnings and invites the next question: What level of future growth would justify paying that price?
That second question is where investing actually begins.
Sources
- Financial Industry Regulatory Authority, Evaluating Stocks.