PEG and growth-adjusted multiples

Here is a question that catches almost every beginner. One stock trades at a price-to-earnings ratio — its price divided by one year's profit per share — of 15. Another trades at 40. Which is cheaper?

The honest answer is that you cannot possibly know yet, and the confident answer — "the 15, obviously" — is the mistake this module exists to cure. A P/E is a price tag with the quantity torn off. Two shops sell rice; one charges ₹15 a bowl and the other ₹40. You would not call the first a bargain until you knew that its bowl was not a quarter the size, or its rice not last year's stock. Earnings are the same. A rupee of profit that will be flat for a decade and a rupee that will treble in five years are simply not the same rupee, and no single P/E can tell them apart.

The PEG ratio is the market's oldest attempt to put the quantity back on the tag. It takes the P/E and divides it by the earnings growth rate. The idea is elegant and, used gently, genuinely useful: it lets you compare the price of growth rather than the price of a single frozen year. But it is also one of the most abused numbers in all of investing, because the moment you divide by a growth rate, the whole answer becomes a hostage to a forecast — and forecasts are guesses wearing decimal points. This module teaches both halves: the honest use, and the quiet abuse.

Return to the two shops. The reason a bare P/E misleads is that it silently assumes the two companies grow at the same rate — and they almost never do. When a fast grower and a slow grower sit side by side, the fast grower should carry a higher P/E, because each of its rupees of profit is the seed of many more. Paying 40 for a rupee that doubles is not obviously worse than paying 15 for a rupee that crawls. The bare multiple, by hiding growth, makes the crawler look cheap and the compounder look expensive, when the truth may be the reverse.

Growth-adjusting is the attempt to make that comparison fair. Instead of price per rupee of current earnings, PEG asks price per unit of earnings growth. A P/E of 40 on a company growing 40% a year is, on this measure, the same "price" as a P/E of 10 on a company growing 10% — both are a PEG of 1.0. The number lets a slow, cheap-looking utility and a fast, expensive-looking software firm finally be laid on the same table without one flattering itself by hiding its growth and the other punishing itself by showing its price.

That is the real service PEG performs, and it is worth respecting: it drags the growth rate out of the shadows and forces it into the open, where you can argue about it. The whole danger, as the rest of this module shows, is that once growth is on the table it looks like a fact — a single tidy number — when it is nothing of the kind. It is a forecast, and usually the least reliable one in the whole valuation. The PEG is only ever as good as the story you can tell about the growth in its denominator.

PEG is deliberately simple. Take the P/E, divide by the expected annual earnings growth rate expressed as a plain number (so 20% growth is written as 20, not 0.20):

PEG = P/E ÷ growth rate (in %).

Work three composite companies, all trading at the same P/E of 30, so that the only thing that differs is growth. illustrative

• Steady Ltd grows earnings at 10% a year. PEG = 30 ÷ 10 = 3.0.
• Middle Ltd grows at 15%. PEG = 30 ÷ 15 = 2.0.
• Quick Ltd grows at 30%. PEG = 30 ÷ 30 = 1.0.

Three companies, one identical P/E, three wildly different verdicts. On the bare multiple they are triplets. On the growth-adjusted view, Quick is paying a rupee of price for a rupee of growth, while Steady is paying three. The single P/E of 30 was hiding a three-to-one difference in what you were actually buying.

Now the more useful direction — the one that overturns a lazy first glance. Put a cheap-looking stock next to an expensive-looking one:

• Value Ltd: P/E 15, growing 8%. PEG = 15 ÷ 8 ≈ 1.9.
• Growth Ltd: P/E 40, growing 30%. PEG = 40 ÷ 30 ≈ 1.3.

On the headline, Value is less than half the price of Growth. On the growth-adjusted view, Value is the more expensive of the two per unit of growth. The naive ranking has flipped. This is the honest gift of PEG: it stops you calling a low-growth company "cheap" just because its P/E is small, and stops you dismissing a fast compounder as "expensive" just because its P/E is large.

A close cousin exists for companies that pay meaningful dividends. The PEGY ratio divides the P/E by growth plus the dividend yield, on the reasoning that a shareholder's total return comes from both. A company on a P/E of 18, growing 9% and yielding 3%, has a PEGY of 18 ÷ (9 + 3) = 1.5, kinder than its plain PEG of 2.0. It is a small refinement, useful mainly for slower, dividend-paying names where ignoring the yield would overstate how dear they look.

Watch a real reading unfold, the way you would do it at your desk. illustrative

A mid-cap consumer company trades at a P/E of 36. A screener has helpfully computed its PEG at 0.8 and coloured it green — "cheap." The temptation is to stop there. Do not.

First, find the growth the screener used. It has taken 36 and divided by 45 — a 45% earnings jump. So the real question is not "is 0.8 cheap?" but "will earnings grow 45% a year?" You go to the record. Revenue over the last three years grew about 12% a year. The 45% came almost entirely from a one-time margin jump: a raw-material cost that collapsed for a year and is already normalising. Strip the one-off and the durable growth looks more like 12–14%.

Recompute honestly. At a 13% durable rate, PEG = 36 ÷ 13 ≈ 2.8 — not cheap at all, roughly three times the "green" figure the screener showed. Nothing about the arithmetic changed. Everything about the answer did, because the input changed from a spike to a sustainable rate. The screener was not lying; it was faithfully dividing by a number that will not repeat.

The discipline is always the same: PEG never answers a question; it relocates it. It moves the whole burden of the valuation onto the growth rate in the denominator, and your job is to go and interrogate that number as if the entire thesis depended on it — because it does.

A PEG is a single number produced by dividing one estimate by another, and it hides at least four things that matter enormously to value.

It cannot see risk. Two companies growing 20% are not equally valuable if one grows steadily and the other lurches. PEG treats a fragile 20% and a bankable 20% as identical, when the market rightly pays far more for the reliable one. A discount rate — the return you demand for taking that risk — is nowhere in the formula.

It cannot see how the growth is bought. A company that grows 20% by reinvesting almost nothing is worth vastly more than one that grows 20% only by ploughing back every rupee of profit into new factories. The first showers cash on owners; the second is a treadmill. PEG counts both as "20% growth" and cannot tell the free-cash compounder from the capital-hungry one.

It cannot see how long the growth lasts. A PEG built on next year's growth says nothing about whether that rate survives three years or ten. Two companies with a PEG of 1.0 today can be worlds apart if one's growth fades to nothing in four years and the other's endures for fifteen. Value lives in the duration of growth, and PEG is blind to it. High growth attracts competition, and competition drags most fast growth back toward the ordinary — usually sooner than the forecast assumes.

It cannot see the quality of the earnings. If the "E" is inflated by aggressive accounting or one-off gains, both the P/E and the growth are corrupted, and the tidy PEG inherits every distortion while looking perfectly clean.

The same handful of PEG errors recur, and each has a simple antidote.

1. Treating PEG = 1 as "fair value." There is no theory that makes 1.0 the line between cheap and dear; it is a rule of thumb Peter Lynch popularised as a screen. A capital-light 25% grower and a capital-heavy one can share a PEG of 1 and differ by half in true value. Use 1.0 as a flag that says "look harder here," never as a scoreboard.

2. Dividing by a spike. The single most common abuse: feeding in one blockbuster year's growth instead of a durable rate. It manufactures a cheap-looking PEG from a number that will not repeat. Always check the forecast growth against the multi-year record.

3. Using the analyst's most optimistic growth. Whoever supplies the denominator controls the answer. A brokerage keen on a stock will pencil in a flattering growth rate, and the PEG obediently turns cheap. Ask whose forecast it is and how often that source has been right.

4. Applying PEG to the wrong kind of company. For a barely-growing utility, a deeply cyclical commodity firm, or a business with negative or erratic earnings, the denominator is meaningless and PEG produces nonsense — huge, negative, or absurdly small. PEG only speaks sense for steady, positive-growth companies.

5. Forgetting that a low PEG can be the market being right. Sometimes a stock's PEG is low because the market quietly doubts the growth will arrive. A "cheap" PEG is occasionally not an opportunity the crowd has missed but a warning the crowd has already priced.