Does a P/E below 20 mean a stock is cheap?

No. It only says the market price is below 20 times the trailing earnings measure used in the calculation. Those earnings may be cyclical, slow-growing, unusually high or difficult to convert into cash.

Why compare low-P/E companies within the same sector?

Sector context reduces one obvious source of difference. Even within information technology, five Nifty 500 companies below 20 times earnings showed very different FY26 growth, return on capital and cash conversion.

What should be checked after a low-P/E screen?

Check how the earnings were produced, whether they are recurring, their growth, cash conversion, balance-sheet risk, return on capital and the business conditions the market may be discounting.

No. It is a useful price-to-earnings relationship and a reasonable screening input. The mistake is asking it to measure business quality, durability, growth and risk at the same time.

P/E Below 20 Worked for Me. Until It Didn’t.

“Buy below 20 times earnings” feels like a complete investing rule because it has a price, a profit and a clean cutoff. It is not complete. It is one question:

How much is the market asking for each rupee of trailing earnings?

It does not tell you how dependable that rupee is, whether it is growing, how much capital produced it or how much of it became cash.

Five FY26 information-technology companies make the limitation visible. All five were current Nifty 500 members and all traded below 20 times trailing earnings on 10 August 2026. Their underlying economics were anything but identical.

Same sector, same rule, five different businesses

Company	Trailing P/E	FY26 ROCE	Total-income growth	PAT growth	CFO / PAT
Wipro	14.08x	18.42%	3.79%	0.47%	1.13x
Zensar Technologies	14.62x	23.53%	8.83%	19.21%	1.00x
Birlasoft	15.53x	21.28%	-1.99%	0.31%	0.93x
Infosys	15.96x	42.65%	9.83%	10.21%	1.15x
TCS	17.62x	65.33%	4.68%	1.35%	1.06x

Source: Altys calculations from consolidated company filings for the year ended 31 March 2026 and adjusted NSE closing prices on 10 August 2026. Nifty 500 membership is as of 9 August 2026. Figures are rounded. P/E uses positive trailing earnings available on the stated date. The companies are neutral illustrations, not a ranking or recommendation. Public source links appear below.

If the rule stops at P/E below 20, every row passes.

But look at what the rule mixes together. FY26 total income declined for Birlasoft and grew nearly 10% for Infosys. PAT was almost flat for Wipro, Birlasoft and TCS, while it grew 19.21% for Zensar. ROCE ranged from 18.42% to 65.33%.

The valuation threshold grouped them. It did not explain them.

What the P/E ratio actually measures

The arithmetic is simple:

P/E = share price / earnings per share

If a share trades at ₹200 and trailing earnings per share are ₹10, the P/E is 20 times.

That calculation is useful. It gives us a common language for the price being paid relative to recent earnings. The problem begins when we silently translate “lower P/E” into “better investment.”

A lower multiple can mean the market has missed something. It can also mean the market expects slower growth, weaker economics, greater cyclicality, a temporary earnings peak or a risk that the ratio does not display.

The ratio reports the price. It does not explain the discount.

Why the denominator can fool you

The “E” in P/E is not a permanent coupon. It is an accounting result for a period.

Four things can make that denominator look safer than it is.

Earnings can be unusually high

A commodity producer near the top of a cycle can report exceptional profit. The high denominator pushes P/E down just when earnings may be hardest to repeat.

Profit can contain a one-time gain

An asset sale, arbitration award, demerger gain or discontinued operation can lift reported profit without improving the recurring business. A mechanically low P/E may disappear when ongoing earnings are separated from the exceptional item.

Growth can be slowing

Two companies can both trade at 15 times earnings. One may be expanding profit, while the other is barely maintaining it. The current ratio does not show the path.

Cash can lag profit

Accrual earnings can rise while receivables, inventory or contract assets absorb cash. P/E treats every rupee of reported earnings alike. Owners eventually experience cash, not the typography of the income statement.

The same low multiple can describe opposite situations

Imagine two companies at 15 times earnings.

	Company A	Company B
PAT growth	15%	-10%
ROCE	35%	12%
CFO / PAT	1.1x	0.4x
Balance sheet	Net cash	High debt

The P/E is identical. Almost every business question is different.

Company A may deserve investigation because the market is underestimating durable economics. Company B may be on a low multiple because the current earnings base is deteriorating or requires more financing than the headline suggests.

The ratio cannot tell us which interpretation is right. It tells us where to start reading.

A better way to use the threshold

Instead of treating P/E below 20 as the answer, turn it into the first stage of a five-part test.

1. Normalise the earnings

Remove clearly exceptional gains and ask whether current profit came from continuing operations. Compare the latest year with several prior years rather than trusting one denominator.

2. Check the direction

Put revenue growth, profit growth and margin movement beside the multiple. A low valuation paired with improving economics is a different proposition from the same valuation paired with erosion.

3. Check the return on capital

ROCE asks how effectively the operating business uses its capital. It does not replace valuation, but it reveals whether similar earnings required very different amounts of capital.

4. Check the cash

Compare operating cash flow with profit over several years. One weak year may be timing. Persistent weak conversion can reveal a business that needs more cash than its income statement suggests.

5. Name the risk the market may be pricing

Write down the most plausible reason for the lower multiple: slowing demand, customer concentration, a cyclical peak, disruption, governance, leverage or capital-allocation concerns. Then look for evidence that confirms or contradicts it.

This is where factor scoring can help. Not by producing one magical score, but by forcing several independent dimensions to sit beside valuation: quality, growth, cash conversion, balance-sheet risk and price.

One factor can identify a candidate. Several factors can reveal the trade-off.

Why “it worked for me” can still mislead

Personal experience is a small and biased sample. Investors remember the low-P/E stock that rerated and forget the one that remained cheap because earnings fell. The failures often leave the watchlist before they leave a vivid memory.

A proper historical test must include every company that qualified at the time, including names that later disappeared, and must use only information that was available on each decision date. Otherwise, a rule can borrow knowledge from the future and call it skill.

The FY26 table above is not such a backtest. It is a current cross-section, used for a narrower point: even on one date, inside one sector, P/E below 20 captured companies with materially different economics.

The practical takeaway

P/E is not the mistake. Stopping at P/E is.

Use a threshold to reduce the market to a researchable list. Then ask:

Are the earnings recurring?
Are revenue and profit improving or deteriorating?
How much capital produces the profit?
Does the profit turn into operating cash?
What risk might explain the multiple?

“Below 20” can open the file. It should never close the case.

Public sources

Related reading:

This article is educational. Altys Labs is not a registered research analyst or investment adviser, and nothing here is investment advice or a recommendation to buy, sell or hold any security.