The P/E ratio and what it actually tells you
Calculate the P/E ratio and explain what high or low values do and do not signal.
Lesson path
Stocks, ETFs, and Equities Macro
Stock Market Fundamentals
Pass the check before saving this lesson.
Pass the check to unlock nextOpen track mapChange starting pointToday's tiny win: make one idea click.
Calculate the P/E ratio and explain what high or low values do and do not signal.
Price-to-earnings, decoded
P/E ratio — price over earnings — is the most quoted number in stock analysis, and also the most misused. The math is simple. Take the share price. Divide by earnings per share (EPS) over the last twelve months. If a stock is $100 and EPS is $5, the P/E is 20. Translation: you are paying $20 today for every $1 the company earned last year.
Why P/E gets quoted everywhere: it is a quick yardstick for how expensive a stock is relative to what it actually produces. The S&P 500 historically averages a P/E in the high teens to low twenties. A stock at 50 P/E is being priced for big future growth. A stock at 7 P/E is being priced as if growth has stalled or risk is high. Same earnings, very different stories.
Two flavors you will see. Trailing P/E uses earnings already reported — past twelve months. Forward P/E uses analyst estimates of the next twelve months. Forward P/E is forward-looking but only as good as the estimates. When analysts are too optimistic, forward P/E looks artificially cheap. When estimates get slashed mid-year, forward P/E suddenly jumps even though price did not change.
Use P/E in context. Compare a tech stock to other tech stocks, a utility to other utilities. A 30 P/E is normal for a fast grower and absurd for a regional bank. Also pair P/E with growth — a P/E of 30 on a company growing earnings 30% a year is very different from a P/E of 30 on a company growing 3%. That ratio of P/E to growth is called PEG, and you will see it once you get past beginner analysis.
What P/E cannot do: tell you when. A stock can stay expensive for years if growth keeps showing up. It can stay cheap for years if no one believes the earnings are sustainable. P/E is a snapshot of market expectations, not a timing signal.
Recap: P/E = price / EPS. It shows dollars paid per dollar of earnings. Low is cheap. Cheap is not automatically good. Always compare within sector and pair with growth.
Knowledge check
Answer before moving on.
1. A stock is $80, EPS over the trailing twelve months is $4. What is the trailing P/E?
2. You spot two stocks. Stock A trades at P/E 8. Stock B trades at P/E 40. Which is the better buy?
3. A company's stock price stays flat, but its forward P/E suddenly drops from 25 to 18. What likely happened?
Pass the check before saving.
Use the knowledge check first. After you pass it, this card turns into the save-and-continue handoff.