Peak profits can make P/E look low
In a cyclical business, unusually strong earnings enlarge the denominator. A low P/E at the peak can rise sharply when profits fall.
Check Compare several years, not just the strongest one.
P/E ratio · four ideas0 of 4 ideas marked read on this device
Free course · Module 6
The P/E ratio: what is a good P/E?
Calculate the multiple, check the earnings and compare it in context.
Compiled by the StockEducation Editorial Team · Reviewed by Associate Professor Charles Lo, CPA, PhD on · Updated 15 Oct 2026 · How we check lessons
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Idea 1 of 4
Divide price by earnings per share.
P/E means price divided by earnings per share. A stock at $50 with annual diluted earnings per share of $2.50 has a P/E of 20. You are comparing the price of one share with the profit attributed to that share. Source 1.
A P/E of 20 means paying $20 for each $1 of annual EPS. It does not mean you will earn 20%, get your money back in 20 years or receive all those profits as dividends.
Share price$50Price of one share
÷Annual EPS$2.50Profit per share
=P/E ratio20×$20 per $1 of EPS
Flip it over: earnings yield
The calculation
Share price ÷ annual earnings per share = P/E.
Marks Idea 1 read on this device
Idea 2 of 4
Compare the same kind of P/E.
There is no universal good P/E. Compare close industry peers and the company’s own history, then ask whether growth expectations, business risk and financing differ. A low multiple can reflect trouble; a high one can depend on optimistic forecasts.
Trailing P/E usually uses the last 12 months of reported earnings. Forward P/E uses forecast earnings, often for the next 12 months. A last-full-year P/E is easy to reproduce from a 10-K, but may be older than a trailing-12-month measure. Label which one you use.
S&P 500 · September 25, 2026
Using the same index price, a lower forward multiple indicates a higher forecast earnings denominator. It does not guarantee that those earnings will arrive. Compare like definitions before drawing that inference.
Why sector and interest rates matter
Before comparing
Same price date. Same earnings definition. Relevant peers.
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Idea 3 of 4
Check the earnings before the multiple.
A P/E is only as useful as the earnings underneath it. Read the income statement, earnings release and notes. Ask whether the year is representative before calling a stock cheap.
Charges and gains change EPS
Apple’s fiscal Q4 2024 diluted EPS was $0.97, or $1.64 excluding a one-time tax charge. That is a quarterly example of why definitions matter; do not use a single quarter as annual EPS. Source 3.
Check Read the reconciliation. An adjusted number is not automatically the better one.
Losses break the usual interpretation
Ford reported a 2025 diluted loss of $2.06 per share. A negative P/E is not evidence of a bargain, and zero EPS makes the ratio undefined. Source 4.
Check Investigate the losses, cash needs and balance sheet.
Same $50 price · different annual earnings
10×EPS $5.00
20×EPS $2.50
50×EPS $1.00
Price stays fixed.Lower earnings → higher P/E
Two more checks: share count and PEG
Ask why
A low P/E is a question to investigate, not a verdict.
Marks Idea 3 read on this device
Idea 4 of 4
Try the calculation, then check the inputs.
Change one assumption and watch the result. This model starts with the hypothetical $50 price and $2.50 annual diluted EPS. Keep the price fixed and change EPS, then reverse the experiment.
Build a P/E and earnings yield
Hypothetical inputsUse matching currencies. Price must be positive. A loss or zero EPS will be explained instead of displayed as a normal P/E.
Calculated P/E20.0×Earnings yield: 5.0%. $50.00 ÷ $2.50 annual EPS.
This calculator performs arithmetic. It does not estimate fair value, choose an earnings forecast or recommend a stock.
Open Compare Stocks Side by Side →Apply it to a company and one close peer
Your research note
Write the price date, earnings period, formula and one reason the result could mislead.
Marks Idea 4 read on this device
Quick check
Three quick checks. Feedback straight away.
Question 1 of 3
A stock trades at $50 and its diluted EPS is $2.50. What is its P/E?
Choose an answer
Choose an answer to see the explanation.
In FactSet’s September 25, 2026 report, why was the S&P 500’s forward P/E (19.2) below its trailing P/E (25.8)?
Choose an answer
Choose an answer to see the explanation.
Ford lost $2.06 per diluted share in 2025. What does that mean for its P/E?
Choose an answer
Choose an answer to see the explanation.
Why can two companies with the same P/E differ?
Review your takeaway card and the learning path
- Calculate it. Divide share price by annual EPS; earnings yield reverses the ratio.
- Label it. Distinguish trailing, last-full-year and forward earnings.
- Compare in context. Use relevant peers and history, then consider growth, rates and risk.
- Check the denominator. Losses, unusual items, cycles and share-count changes can mislead.
Reading markers and these practice checks stay on this device. They do not mark the LMS lesson complete.
Sources and assumptions
- Investor.gov, Price-earnings ratio. SEC investor education definition and comparison context.
- FactSet, Earnings Insight, September 25, 2026. Page 15: dated trailing, forward, historical and sector P/E measures.
- Apple, fiscal Q4 2024 results, October 31, 2024. Reported diluted EPS of $0.97 and $1.64 excluding the specified charge; quarterly figures.
- Ford, fiscal 2025 Form 10-K. Reported diluted loss of $2.06 per share.
The $50 share price and $2.50 EPS are hypothetical teaching inputs. Historical index and company disclosures are dated, not live prices or forecasts. Ratios and estimates are not investment recommendations. Local practice does not complete the LMS lesson or record a grade.
StockEducation provides general education, not personal financial, tax or legal advice. Nothing here recommends a specific security. Investing involves risk, including loss of money you invest.
