You're looking at a stock. The price is $50. Is that expensive? Cheap? Completely random? Without context, a share price tells you almost nothing. That's where the P/E ratio comes in.
The Price-to-Earnings ratio is one of the most commonly used metrics in investing, and for good reason. It's the quickest way to get a sense of whether the market thinks a company is worth what it's charging. Once you understand it, you'll start seeing it everywhere.
what is the P/E ratio?
P/E stands for Price-to-Earnings. It tells you how much investors are willing to pay for each dollar of a company's profit. Investopedia's P/E guide covers the technical detail, but here's the simple version:
EPS is how much profit a company makes for each share of stock. If a company made $10 million in profit and has 5 million shares, EPS is $2.
a real example that makes it click
Let's say you're comparing two companies on the ASX:
TechCo
Share price: $100
EPS: $2
P/E = 50
BigBank
Share price: $40
EPS: $4
P/E = 10
Investors pay $50 for every $1 of TechCo's earnings. They pay $10 for every $1 of BigBank's earnings. Does that mean TechCo is overpriced and BigBank is a bargain? Not necessarily.
TechCo's high P/E might mean investors expect its earnings to grow rapidly. They're paying more now because they think those $2 of earnings will be $10 in a few years. BigBank's low P/E might mean it's a stable, mature business with slow growth. The market isn't expecting much change.
The P/E ratio doesn't tell you which company is "better." It tells you what the market expects.
high P/E vs low P/E
| high P/E (25+) | low P/E (under 15) | |
|---|---|---|
| What it signals | Market expects strong future growth | Market expects slow or no growth |
| Optimistic read | Earnings will grow into the valuation | Undervalued, potential bargain |
| Pessimistic read | Overvalued, overhyped | Declining business, value trap |
| Typical sectors | Tech, biotech, clean energy | Banks, utilities, mining |
what's a "good" P/E ratio?
There's no universal answer. It depends entirely on context. Comparing P/E ratios across different industries is like comparing the price of a coffee to the price of a car. They're measuring completely different things.
| sector | typical P/E range | why |
|---|---|---|
| Technology | 25-60+ | High growth expectations, innovation premium |
| Clean energy | 20-50 | Structural growth tailwind, government support |
| Banks | 10-15 | Mature, regulated, steady earnings |
| Mining | 8-15 | Cyclical, earnings swing with commodity prices |
| Utilities | 12-18 | Defensive, slow growth, reliable dividends |
The right comparison is always within the same sector, or against a company's own historical P/E. If a bank that normally trades at 12x suddenly trades at 20x, something unusual is going on. If a tech company usually at 40x drops to 20x, it might be worth investigating.
the three comparisons that actually matter
- Industry peers. Compare a company to others in its sector. A P/E of 30 is expensive for a bank but normal for a software company.
- Its own history. If a company's P/E is way above or below its 5-year average, ask why. Did something change, or is the market overreacting?
- The broader market. The ASX 200 typically trades at a P/E between 14 and 18. If a company is trading far above or below that, there should be a clear reason.
what P/E doesn't tell you
P/E is useful but incomplete. Here's what it misses:
- Debt. A company might look cheap on a P/E basis but be buried in debt. Profits can look healthy right up until the interest payments become unsustainable.
- Future earnings trajectory. P/E uses past or trailing earnings. But investors are buying the future. A company might have a high P/E because earnings are about to double, or a low P/E because earnings are about to halve.
- Accounting differences. Different companies can calculate earnings differently depending on their accounting standards. This is especially true when comparing companies across countries. An Australian company using IFRS and a US company using GAAP might report different earnings for the same underlying business.
- One-off events. A huge sale of assets or a legal settlement can inflate or deflate earnings for a single quarter, making the P/E misleading.
This is why experienced investors always pair P/E with other metrics. On its own, it's one piece of the puzzle. With EBITDA, cash flow, and debt ratios alongside it, you get a much fuller picture.
pairing P/E with other tools
| metric | what it adds | where to learn more |
|---|---|---|
| EBITDA | Operating profitability before debt, tax, and accounting | our guide |
| Debt-to-equity | How much the company relies on borrowed money | Investopedia |
| Free cash flow | Actual cash available after all spending | MoneySmart |
| PEG ratio | P/E adjusted for growth. Under 1 may signal undervaluation. | Investopedia |
how this connects to impact investing
Here's something most P/E guides won't tell you: a "good" valuation means nothing if the company is making money by cutting corners on workers, dumping waste, or lobbying against climate action.
At inaam, when we evaluate companies for the portfolio, we look at financial metrics like P/E alongside impact data. A company might look attractively priced on paper, but if its profits come from practices that harm communities or the environment, it doesn't make the cut. You can see exactly how we screen companies in our methodology.
The RIAA publishes benchmark data showing that responsible investment funds in Australia have consistently matched or outperformed their conventional peers. So it's not a trade-off. You don't give up returns to invest with values.
what to remember
- P/E is a starting point, not a verdict. It tells you what the market expects. Not what will actually happen.
- Always compare within context. Same industry, same region, same time period.
- High doesn't mean overpriced. It might mean high growth. Low doesn't mean cheap. It might mean declining.
- Pair it with other metrics. EBITDA, cash flow, and debt levels give you the full picture.
- Consider what's behind the earnings. Profits built on exploitation or environmental damage aren't sustainable.