P/E Ratio: What This Multiple Tells You (and What It Doesn't)
Few financial ratios get more airtime than the P/E ratio—and few are more frequently misunderstood. You see it in analyst reports, investor presentations, acquisition discussions, and casual conversations about whether a business is “expensive” or “cheap.” It’s simple enough to quote in a sentence, which makes it easy to deploy confidently and incorrectly at the same time.
This article is about using the P/E ratio properly: understanding what it actually measures, what it doesn’t, and the questions you need to ask before treating it as a meaningful signal.
What the P/E ratio actually measures
The price-to-earnings ratio is a simple fraction: the market price of a share divided by the company’s earnings per share (EPS).
P/E = Price per share ÷ Earnings per share
Or equivalently, for the whole company:
P/E = Market capitalisation ÷ Net profit
What does this number mean in practice? It tells you how many euros (or dollars, or whatever currency) investors are paying today for each euro of current annual earnings. A P/E of 15 means investors are paying €15 for every €1 of annual net profit the company generates.
There’s another way to read it: the P/E is roughly the number of years it would take, at the current earnings level, for cumulative profits to equal the price paid—assuming profits stay constant. A P/E of 20 means you’re paying a price equivalent to 20 years of current earnings.
This second interpretation reveals something important: the P/E is inherently forward-looking in the market’s mind, even when calculated on trailing earnings. Investors pay more than current earnings justify because they expect those earnings to grow. They pay less when they expect earnings to fall or stagnate.
The two types of P/E you’ll encounter
Trailing P/E (TTM — Trailing Twelve Months): The most common version. Uses the last twelve months of reported earnings. It’s concrete and based on real numbers, but it looks backward.
Forward P/E: Uses analysts’ estimates of next year’s (or next period’s) earnings. More relevant for forward-looking decisions, but built on projections that may or may not materialise.
Neither is inherently better. Trailing P/E tells you what you’re paying relative to what the company has actually earned. Forward P/E tells you what you’re paying relative to what people expect the company to earn. Both are useful; both have limitations.
What a “high” or “low” P/E actually means
The most common mistake with P/E is treating the number in isolation. A P/E of 8 isn’t automatically cheap. A P/E of 35 isn’t automatically expensive. The number only means something in context.
Context 1: The sector
Different industries trade at structurally different P/E levels because their growth profiles, capital requirements, and earnings stability differ. Technology companies with high growth potential and scalable models have historically traded at much higher P/Es than utilities, which have stable but slow-growing earnings. Comparing the P/E of a software company to that of a regional airline and concluding one is cheaper than the other misses the point entirely.
A more useful question: how does this company’s P/E compare to its sector peers? A P/E of 12 in a sector that averages 20 might signal undervaluation—or it might signal the market knows something about this specific company’s prospects that justifies the discount.
Context 2: The economic cycle
P/E ratios expand and contract with economic cycles. During recessions, earnings often fall faster than prices (markets anticipate recovery), which temporarily inflates P/E ratios—making companies look more expensive precisely when they may be most attractive. During booms, earnings are high and P/Es can look deceptively moderate.
This is why comparing P/E across different periods in the cycle without adjustment gives misleading signals.
Context 3: Interest rates
The P/E ratio doesn’t exist in a vacuum—it competes with other investments. When interest rates are low, investors accept lower earnings yields (higher P/Es) because the alternative of holding bonds yields little. When rates rise, the relative attraction of equity earnings declines, and P/Es tend to compress. This is one reason why the same P/E level that seemed reasonable in a low-rate environment can look stretched when rates are higher.
Context 4: Quality of earnings
Two companies can have identical P/Es with very different underlying realities. One might have recurring, cash-generative, predictable earnings. The other might have earnings inflated by one-off items, accounting choices, or revenue recognition policies that won’t sustain. The P/E sees both as equivalent. You shouldn’t.
The limitations that matter most
P/E doesn’t work for loss-making companies. If a company has negative earnings, the P/E is either negative or undefined. This eliminates it from the analysis of startups, turnaround situations, or businesses in cyclical troughs—often exactly the cases where valuation questions are most pressing.
Earnings can be manipulated more easily than cash flows. Net profit is an accounting construct that reflects choices about depreciation, provisioning, revenue recognition, and other items. Two companies with identical operating performance can report different earnings depending on their accounting policies. This is why many analysts prefer EV/EBITDA or price-to-cash-flow multiples for comparisons across companies with different accounting approaches.
P/E ignores the balance sheet. A company trading at a low P/E might be carrying enormous debt that will consume future earnings. A company with a high P/E might have net cash that makes the effective earnings multiple much more modest when you account for it. Enterprise value multiples (which include debt and subtract cash) give a more complete picture for this reason.
Historical P/E averages are context-dependent. “The market average P/E is 15, so anything below that is cheap” is not a useful heuristic. Market average P/Es have varied enormously across decades and geographies, and the composition of markets changes over time. What was the average in one era tells you relatively little about the appropriate level in another.
P/E in the context of private business valuation
The P/E ratio is most naturally discussed in the context of listed equities. But it also appears—sometimes with modifications—in private business transactions.
For owner-managed businesses, aviation schools, and small operators considering an acquisition or a valuation exercise, a version of the P/E logic shows up in conversations about “earnings multiples.” A business being acquired for “5x earnings” or “8x net profit” is using P/E-equivalent logic.
A few things to keep in mind when applying this to private businesses:
The earnings figure needs scrutiny. In owner-managed businesses, reported net profit often reflects the owner’s compensation choices, related-party transactions, and expenses that would change under new ownership. A meaningful earnings multiple needs to be applied to a normalised earnings figure—one that strips out the idiosyncrasies of the current owner’s management.
Multiples are lower for private businesses. Private companies trade at a discount to equivalent listed businesses because of illiquidity, concentration risk, dependence on key individuals, and lower transparency. An industry trading at a listed P/E of 18 might support private transaction multiples of 5–8x earnings for smaller operators.
Sector comparables are scarce in niche industries. In aviation maintenance, flight training, or specialised aerial work, there may be relatively few comparable transactions. The multiples derived from broader financial services or transport comparables need adjustment for the specific characteristics of the business being valued.
Growth expectations drive the multiple. A flight school with a clear growth trajectory, a diversified client base, and strong regulatory standing will command a higher multiple than one with flat or declining revenues, key-person dependence, and a fleet approaching end-of-life. The multiple isn’t just a market average—it should reflect the specific risk and growth profile of this business.
How to use P/E without getting trapped by it
The P/E ratio is most useful as a first filter and a conversation starter, not as a final answer.
When you see a P/E figure—whether on a listed company you’re considering investing in or a private business you’re evaluating—the useful questions are:
- What earnings figure is this based on? Trailing? Forward? Normalised?
- How does it compare to sector peers? Is there a clear reason for any premium or discount?
- Where are we in the economic and sector cycle? Are current earnings unusually high or low?
- What assumptions about growth are embedded in this multiple? Do those assumptions seem reasonable?
- What does the balance sheet look like? Is debt or cash materially affecting the picture?
- Are there any accounting choices that make earnings look different from underlying cash generation?
None of these questions are difficult. But skipping them—and treating the P/E number as a self-contained verdict—is where the ratio does its most damage.
A note on what matters more
In most serious valuation exercises—acquisitions, private equity transactions, strategic decisions about business value—the P/E is a crosscheck, not the primary analysis. Discounted cash flow analysis, asset-based approaches, and sector-specific multiples (EV/EBITDA, EV/Revenue, EV/EBIT) typically carry more weight in rigorous valuations.
The P/E is useful for a quick orientation—a way of contextualising whether a price is in the right neighbourhood. It’s poor at capturing the nuances that determine whether a specific price, for a specific business, at a specific moment, makes sense.
If you’re using P/E in the context of evaluating a business acquisition, assessing the value of an existing operation, or benchmarking your own company against market expectations, the ratio is a useful starting point. But the analysis worth doing lives in the questions you ask after you’ve seen the number—not in the number itself.