What is P/E?
The price-to-earnings ratio (P/E, also called PER) tells you how many times annual earnings per share the share price represents. EPS is accounting profit attributable to each common share. It is not the dividend paid into your account.
P/E = share price ÷ earnings per share (EPS)
KRW 50,000 ÷ annual EPS of KRW 5,000 = 10 times earnings. You pay 10 units of price for one unit of annual earnings. The SEC financial statement guide explains this formula.
A P/E of 10 does not guarantee that you recover your investment in 10 years. Companies do not pay all their profit to shareholders. Future earnings and the price at which you sell can also change.
How do you calculate P/E?
Divide a KRW 50,000 share price by annual EPS of KRW 5,000 to get 10. You can also calculate it for the whole company: KRW 500 billion in market capitalization ÷ KRW 50 billion in annual net income = a P/E of 10.
In actual filings, differences in share counts and the scope of earnings can make the two results differ.
One Apple share price, two P/E ratios?
The same Apple stock on the same day gives P/E ratios of 36.66 and 33.02. The price is identical. The difference is whether earnings include a one-time tax charge.
| Earnings basis | Annual diluted EPS | P/E |
|---|---|---|
| Reported earnings (GAAP) | $6.08 | 36.66× |
| Tax charge excluded (company-adjusted non-GAAP) | $6.75 | 33.02× |
Apple reported EPS of $6.08, or $6.75 after the company's adjustment to exclude this charge. The adjustment removes an expense from the same historical earnings. It is not a forecast of future profit.
EPS period: October 1, 2023–September 28, 2024. A historical example, not current P/E. Sources: Apple IR stock price · official statements, pages 1 and 4.
Removing the expense lowers P/E. But if an excluded cost could recur, adjusted EPS alone can make the stock look cheaper than it is.
Apple sources and calculation details
The calculation uses the October 31, 2024 earnings release and the next trading day's close. The one-time tax charge relates to the EU State Aid decision. Apple's reconciliation shows the adjustment.
The price is the $222.91 Closing Price from Apple IR's historical lookup, not a dividend-adjusted close. Divide by the published EPS rounded to cents, then round P/E half up to two decimal places. Amounts are USD, with no currency conversion.
Can P/E rise without a share price increase?
At KRW 50,000, EPS of KRW 5,000 gives a P/E of 10. If EPS falls 50% to KRW 2,500, P/E rises 100% to 20. The stock price did not rise. The same price now buys less earnings.
| EPS | P/E |
|---|---|
| 10,000 | 5.00 |
| 5,000 | 10.00 |
| 2,500 | 20.00 |
| 1,000 | 50.00 |
Change the price and EPS to calculate P/E
Leave price at 50,000 and change EPS to 2,500. The result below becomes 20 times. The chart above remains a fixed KRW 50,000 illustration.
P/E:
Amounts are KRW, with no currency conversion. Results are rounded half up to two decimal places. EPS at or below zero is marked as not meaningful.
Does low P/E always mean undervalued?
In cyclical industries such as steel, shipping and semiconductors, a boom can lift earnings and lower P/E. Can the company keep earning as much as it does in its best years?
Keep the fictional share prices of A and B fixed, and replace past-year earnings with next-year forecasts. Both companies use the same price date and next-12-month forecast period.
| Company | Price | Past EPS → P/E | Expected EPS → P/E |
|---|---|---|---|
| A | 50,000 | 10,000 → 5× | 2,000 → 25× |
| B | 30,000 | 1,000 → 30× | 2,000 → 15× |
A initially looked much cheaper. But if A's earnings are expected to fall 80% and B's to double, A becomes 25 times and B becomes 15 times: the ranking reverses. The question is whether B can actually double its earnings. If growth disappoints, paying 30 times past earnings can prove costly.
On peak-cycle earnings and normalized EPS: CFA Institute's valuation reading.
How do trailing and forward P/E differ?
| Measure | Denominator | Limitation |
|---|---|---|
| Trailing P/E | Actual EPS over the last 12 months (TTM) | Past booms and one-time items remain. |
| Forward P/E | Expected EPS | The ratio changes when estimates change. |
Suppose your stock app shows a trailing P/E of 10 and a forward P/E of 8. With the same price and earnings definition, the forecast assumes higher profit. At KRW 50,000, past EPS of 5,000 gives 10 times earnings; forecast EPS of 6,250 gives 8.
If that earnings forecast falls, the multiple of 8 rises even without a price change. Forward earnings may cover the next 12 months, this fiscal year or the next fiscal year. Match the forecast period and estimate date before comparing.
How should you interpret P/E for a loss-making company?
At zero EPS, division is undefined. Negative EPS can produce a negative mathematical ratio, but it does not mean the stock is cheaper than a positive P/E of 5. Nor can −5 and −30 be ranked like ordinary positive multiples.
For a loss-making company, start with two questions: when could it turn profitable, and does it have enough cash to get there? Growing revenue may still come with faster cash depletion and a need for new funding.
P/S, P/B or EV/EBITDA can provide context in some industries. But revenue, book value and EBITDA are not the same as net income or cash left over.
Can companies with the same P/E have different appeal?
Consider two fictional companies. One earns KRW 5,000 per share by selling its products. Another earns 2,500 from its business and adds a 2,500-per-share gain from selling an asset. At a KRW 50,000 share price, both report a P/E of 10.
What if the second company cannot repeat that asset sale? Using only its recurring EPS of 2,500 gives a P/E of 20. The same reported multiple hides different future earning power. The Apple example works in the opposite direction: a one-time expense raises reported P/E.
Growing and shrinking businesses also deserve different scrutiny. So do companies with strong margins and those facing heavy interest costs. Capital spending needs vary by industry. The cash flow statement helps show whether reported profit turns into cash.
To understand cash paid to shareholders, continue with dividend yield and the payout ratio.
How can you use P/E in investment analysis?
Suppose a stock you follow trades at 8 times earnings while a peer trades at 12. First match the price date, earnings period and EPS definition. If the gap remains, ask why investors pay less for this company's earnings.
Look for an asset sale that lifted profit or a forecast of declining earnings. Then review the company's own historical P/E range. Separate boom years, downturns and loss periods so a past average does not create a false impression of cheapness.
Finally, test a lower earnings forecast. In the simulator above, leave price at KRW 50,000 and cut EPS from 5,000 to 4,000. P/E rises from 10 to 12.5. A 20% EPS cut raises P/E by 25%. Consider whether your reason for buying still holds under that change.
For a real company's historical performance, read the Apple ten-year investment analysis. Change periods in the investment backtest and use CAGR and MDD to examine returns and declines together. Past returns do not establish that today's P/E is fair.
Comparison guidance and limitations: Charles Schwab's P/E guide.
Frequently asked questions
What is a good P/E ratio?
There is no universal number. Start with industry peers and the company's history, then consider growth, interest rates, debt and sustainable earnings. A P/E below 10 is not automatically cheap.
Why do brokers show different P/E ratios?
Price timestamps, TTM or forecast periods, basic or diluted EPS, and adjustments for one-time items may differ. Check the earnings definition and date before comparing values.
Does a P/E of 10 pay me 10% a year?
No. Its reciprocal, 10%, is accounting earnings relative to the share price. It is neither dividend yield nor the total return an investor will earn.
Where can I find a stock's P/E?
Check an exchange or broker's stock page, then verify EPS and its period in company IR, DART or SEC filings. For Korean companies, also check consolidated versus separate accounts and income attributable to controlling shareholders.