P/E ratio explained: price, earnings and earnings yield
The price-to-earnings ratio divides the share price by earnings per share (EPS), or equivalently market capitalization by net income. A P/E of 20 means investors pay $20 for each $1 of annual profit. Use diluted EPS, so that options and convertible securities are counted.
Turn it upside down and you get the earnings yield, EPS ÷ price: a P/E of 20 is a 5% earnings yield and a P/E of 10 is 10%. The yield invites a comparison with bonds, with one important difference. A bond's coupon is fixed, while a company's earnings can grow, shrink or vanish. When a stock's earnings yield sits below a government bond yield, the price is betting on growth; and because profits are less certain than a government's promise, they normally need a higher yield, meaning a lower P/E, to compensate. That is also why higher bond yields tend to weigh on P/E multiples, all else equal: investors demand more from every asset.
A useful anchor: a business that will never grow and pays out all its earnings is worth its earnings divided by the required return. At a 9% required return that is 1 ÷ 0.09, about 11 times earnings. Anything above that is a payment for growth.
What is a good P/E ratio? Translate it into implied growth
The most useful test of a P/E is the growth it requires. The table uses a simple two-stage model (illustrative). It takes the forward P/E, price ÷ next year's EPS; earnings grow at a constant rate for ten years, then 3% a year forever; and every reinvested dollar earns 25%, so a company growing 10% must retain 40% of its earnings (10 ÷ 25) and can pay out the rest. The model solves for the ten-year growth rate that makes the price fair at three required returns.
| Forward P/E | Earnings yield | Implied growth, 8% required return | At 9% | At 10% |
|---|---|---|---|---|
| 10 | 10.0% | −9.4% | −6.1% | −2.9% |
| 12 | 8.3% | −4.9% | −1.5% | 1.9% |
| 15 | 6.7% | −0.1% | 3.5% | 7.0% |
| 20 | 5.0% | 5.4% | 9.3% | 13.1% |
| 25 | 4.0% | 9.4% | 13.5% | 17.5% |
| 30 | 3.3% | 12.6% | 16.8% | 21.0% |
Three readings follow. First, at a 9% required return a P/E of about 13 prices in no growth for a decade, so lower multiples imply shrinking earnings or higher perceived risk. Second, the required return matters as much as the multiple: a P/E of 20 asks for 5.4% annual growth at 8% but 13.1% at 10%. Third, the quality of growth matters. If reinvested earnings return 15% rather than 25%, a P/E of 20 at 9% requires 14.5% growth instead of 9.3%, because more of each dollar of profit must be ploughed back.
A good P/E, then, is one whose implied growth sits comfortably below what the business can plausibly deliver. The implied growth rate guide applies the same idea to free cash flow.
Forward P/E vs trailing P/E
Trailing P/E uses the last twelve months of reported EPS. Forward P/E uses analysts' estimates for the next twelve months or fiscal year. Illustrative: a $60 stock that earned $3.00 over the past year trades at 20 times trailing earnings; if analysts expect $3.75 next year, 25% growth, its forward P/E is 16.
| Trailing P/E | Forward P/E | |
|---|---|---|
| Earnings used | Reported, last 12 months | Consensus estimate, next 12 months or year |
| Strength | Actual reported figures | Reflects where the business is heading |
| Weakness | Misleads when earnings are changing fast | Estimates can be wrong and are revised often |
| Most useful for | Stable businesses | Companies whose earnings are shifting quickly |
Check the earnings basis too. Many companies report "adjusted" EPS that excludes stock-based compensation, amortization and restructuring costs, so a forward P/E on adjusted figures can look far lower than a trailing P/E on GAAP figures. Compare like with like.
Cyclicals: why the P/E is lowest at peak earnings
For cyclical companies such as miners, chemical makers, carmakers and chipmakers, the P/E often moves opposite to value. Illustrative: a $60 stock trades at 6 times peak EPS of $10, 12 times mid-cycle EPS of $5 and 40 times trough EPS of $1.50. The market prices the whole cycle, so the lowest P/E tends to appear just as profits are about to fall, and the highest near the bottom.
Use normalized earnings instead: average margins over a full cycle applied to today's revenue, or several years of average EPS. Price-to-book is a second check for capital-heavy cyclicals. A low multiple on record margins is a classic value trap pattern.
Negative or near-zero earnings
When EPS is negative the P/E is not meaningful, and most data sources show it as blank or "n/m". When EPS is close to zero the ratio explodes and becomes unstable: a $40 stock earning $0.20 trades at 200 times earnings, and at 100 times if earnings merely rise to $0.40. Neither figure says much about value.
For these companies, use measures that do not hinge on a thin profit line: EV/sales judged against a realistic target margin, EV/EBIT on normalized margins, or a reverse DCF that solves for the revenue growth needed to reach a mature margin.
Depressed earnings can also be deliberate. A company spending heavily on research or customer acquisition, which accounting treats as an expense, can show a high P/E on profits that understate its mature earning power. Estimate what margins look like once that spending normalizes before judging the multiple.
The PEG ratio and its limits
The PEG ratio divides the P/E by the expected annual EPS growth rate in percent, so a stock at 30 times earnings expected to grow 15% has a PEG of 2. A common rule of thumb treats a PEG near 1 as fair. The same model shows why that rule breaks down (illustrative, 9% required return):
| Ten-year EPS growth | Justified forward P/E | Justified PEG |
|---|---|---|
| 5% | 16.1 | 3.2 |
| 10% | 20.8 | 2.1 |
| 15% | 27.2 | 1.8 |
| 20% | 35.9 | 1.8 |
The fair PEG is not constant. Slow growers justify high PEGs because much of their value comes from earnings that continue and are paid out, not from growth, and dividing by a small growth rate inflates the ratio. None of these rows comes close to a PEG of 1. PEG also ignores how long growth lasts, how much capital it consumes, the required return and the balance sheet, and it usually rests on a growth estimate covering only a few years. Treat it as a quick comparison between similar companies, not a valuation.
How to judge a P/E in practice
- Confirm the earnings: trailing or forward, GAAP or adjusted, and free of one-off gains.
- Normalize for the cycle if the business is cyclical.
- Compare with the company's own history and its sector, not the whole market. Software firms, banks and utilities trade on different multiples for good reasons.
- Translate the P/E into implied growth and set it against the company's record and consensus forecasts.
- Check the balance sheet. P/E ignores debt, so cross-check with EV/EBIT, as explained in how to value a stock.
VALYSTR's screener lets you combine a P/E filter with growth, return-on-capital and debt rules, so a low multiple has to come with a business that can support it.
Screen P/E alongside growth and quality
Combine a P/E filter with growth, return-on-capital and balance-sheet rules, or describe the screen you want in plain words.
Frequently asked questions
Is a P/E ratio of 15 good?
It depends on the company. In the illustrative model in this article, a forward P/E of 15 implies about 3.5% annual earnings growth for ten years at a 9% required return. That is undemanding for a healthy, growing business but too much for one in decline. Check what growth the business can deliver, whether earnings are cyclical, and how much debt it carries.
Is a high P/E ratio bad?
Not by itself. A high P/E means the price assumes strong growth, a low required return, or both. That can be justified for a company with a long runway and high returns on the capital it reinvests. The risk is that high expectations leave little room for disappointment, so compare the implied growth with the company's record and with forecasts.
What is the difference between forward P/E and trailing P/E?
Trailing P/E divides the share price by the last twelve months of reported earnings per share. Forward P/E divides it by analysts' estimates for the next twelve months or fiscal year. Trailing uses actual figures but looks backward; forward is more relevant when earnings are changing quickly, but it depends on estimates that can prove wrong.
What is a good PEG ratio?
A PEG near 1 is a popular rule of thumb for fair value, but it has no firm theoretical basis. Slow-growing companies can justify PEGs well above 1, and the ratio ignores how long growth lasts, how much capital it needs and the balance sheet. Use it to compare similar companies quickly, not to decide what a stock is worth.
Why do some stocks have no P/E ratio?
A P/E is not meaningful when earnings per share are negative, so most data sources leave it blank. When earnings are close to zero the ratio becomes huge and unstable. For these companies, look at EV/sales against a realistic target margin, normalized operating earnings, or a reverse DCF that solves for the revenue growth the price requires.