P/E Ratio Basics
Price divided by Earnings Per Share. Shows how much investors pay for each rupee of earnings.
Interpretation
- Low P/E: Potentially undervalued
- High P/E: Growth expectations
- Negative P/E: Company losing money
Comparison
- Compare within sector
- Compare to historical P/E
- Compare to market average
Options Application
Low P/E stocks for covered calls. High P/E stocks for protective puts.
What the P/E Ratio Actually Tells You
The price-to-earnings ratio divides the market price of a share by its per-share profit, summarising how many years of current earnings the market is paying for. A P/E of 25 on an IT major means investors expect 25 years of current profit embedded in the price; a P/E of 8 on a PSU bank signals the opposite: the market is discounting the earnings stream heavily, often because of asset quality doubts.
Trailing vs Forward P/E
Trailing P/E uses the last four reported quarters, while forward P/E uses analyst forecasts for the coming four. The gap between them is the growth premium priced into the stock. A wide gap between a cheap trailing P/E and a dear forward P/E can mean either strong expected growth or hopelessly aggressive forecasts; always read the forecast source before acting on the forward number.
P/E Is Meaningless in the Case of Loss-Making Companies
When earnings are negative, the ratio is negative or undefined, and comparing loss-makers by P/E is academically empty. For such names, use price-to-book, price-to-sales or enterprise value to operating cash flow instead. New-age Indian listings frequently trade through their entire P/E range instantly on the first profitable quarter, so an EBITDA-based comparison is the practical substitute.
Sector-Relative, Not Cross-Sector
A 28 P/E is cheap for a high-margin software exporter and expensive for a capital-intensive refiner. Compare a stock only against its own sector median and its own three-year average. When a stock trades at a 30% discount to its sector while its return on equity holds up, that is the classic mispricing an options trader can exploit with a long call or a put spread depending on the direction of the re-rating.
Building a Screening Routine
- Start with the sector list and the current sector median P/E.
- Exclude cyclicals at the peak of their earnings cycle to avoid the 'cheap P/E at the top' trap.
- Filter for P/E below the sector median and ROE above 15%.
- Confirm the earnings used are recurring, stripping one-off gains.
The Options Angle
Implied volatility of a stock is partly a function of its earnings uncertainty, and P/E compression coming out of such announcements is often the catalyst options buyers need. If a fundamentally cheap stock pairs a deep-volatility spike with a decelerating P/E dip, the re-rating often continues for several weeks; a call spread entered after the initial pop captures the drift with limited downside.
Earnings Yield and the Bond Analogue
Flipping the P/E ratio gives the earnings yield: the E/P tells you how much annual earnings you buy for every rupee of price. When the Nifty 50 trades at a trailing P/E near 22, the index earnings yield is roughly 4.5 percent, which must be compared with the 10-year government bond yield hovering near 6.5 to 7 percent on the Indian curve. That gap, the earnings yield minus the bond yield, is the equity risk premium, and it is the single most useful decompression of the raw P/E number. A thin or negative premium signals expensive markets, while a premium above 3 percent usually marks a workable buying regime for long-term accumulation programmes.
PEG Ratio: Growth-Adjusted Valuation
Divide the forward P/E by the expected earnings growth rate to get the PEG ratio. A stock carrying a 28 forward P/E but earning a 20 percent earnings CAGR lands at a PEG of 1.4, which is reasonable, while a defensive stock at 32 times with a 6 percent growth run shows a PEG above 5 and prices in pure safety. In Indian stock selection the PEG works best on midcaps and IT exporters, where growth estimates are available from consensus reports; it is nearly useless on cyclicals whose next-year earnings are a guess.
Cyclicals, Defensives, and Sector-Normalised P/E
Compare valuation within a sector, not across sectors. A bank at 3.5 times book is normal; an IT firm at 3.5 times book is a screaming buy; a metal stock at 3.5 times book is either the first leg of an up-cycle or a trap. Build a simple table per sector with the median trailing P/E over five years, then mark a stock as cheap only when it sits below its own sector's median. This normalisation removes the biggest P/E mistake, which is judging Tata Motors against Hindustan Unilever when the two sectors never trade on the same multiple at the same time.
Where the Ratio Lies in India
Three Indian realities distort the raw P/E. First, interest and depreciation distortions in manufacturing firms inflate or depress earnings unpredictably. Second, the largest banks cannot be valued on P/E cleanly because provisions make net profit a managed number; price-to-book is the honest multiple there. Third, promoter-group companies with treasury gains flatter earnings in a bull year. For each candidate stock, verify that the E in the P/E comes from operating profit, not one-off items, before adding the name to any screen.
Backtesting a P/E Screen Simply
You can test the discipline with a 60-line Python script: pull trailing P/E for the Nifty 200 universe from a free screener at monthly frequency, sort each month into deciles by P/E, and hold each decile for the following month. Over a five-year test window the cheapest decile historically earns more than the most expensive decile before costs, but the spread narrows to near zero once you subtract the survivorship of the universe itself. Use the equity curve as evidence, then layer the valuation tilt on top of a momentum screen rather than trading value alone.
- Pull the sector-median P/E as the first filter.
- Confirm the earnings are operating earnings, not one-off gains.
- Compare E/P against the 10-year G-Sec yield.
- Add a PEG check for growth names.
- Enter a small index position rather than one stock when the market itself is at extremes.
Dividend Yield: The P/E's Quiet Counterweight
Pair the P/E with the dividend yield, because the two answer the same equation from opposite sides: a low P/E with a healthy dividend yield is a stock paying the investor to wait, while a low P/E with no dividends is a stock asking the investor to wait for free. On Indian names the yield adds the cash-flow test the ratio alone cannot supply - a screen that demands both a P/E below the sector median and a dividend yield above the index average filters out accounting-flattered cheap stocks and keeps the genuinely cash-generative ones. Recalculate both on the quarterly result date, because the yield reprices the moment the payout decision is announced, and a screen that ignores the dividend calendar is a screen that misreads the re-rating.
