Walk into any conversation about stocks and within thirty seconds someone will mention PE ratio. It gets thrown around as if it settles arguments: "too expensive, PE is 80" or "great value, PE is only 12." Most people using it have no idea why those numbers matter, or when they are completely misleading.
PE stands for price-to-earnings. The price part is straightforward: what one share costs right now on the exchange. The earnings part is the company's net profit divided by total shares, giving you earnings per share (EPS). Divide the share price by EPS and you get the ratio.
Think of PE as how many years of current profits you are paying for upfront. A PE of 20 means you are paying twenty years of today's earnings. If nothing changes and the company returns all its profits as dividends, you break even in twenty years. Obviously things do change. Companies grow, shrink, get disrupted, acquire competitors. Which is exactly why PE is a starting point, not a conclusion.
When high PE makes complete sense
HDFC Bank traded at 30 to 35 times earnings for most of the decade before 2022. Every year, analysts called it expensive. Every year, the bank grew its earnings at 18 to 20 percent, and the stock kept compounding. Investors who avoided it because the PE looked high missed one of the most reliable wealth creators in Indian market history.
The logic is simple. If a company is growing earnings at 25 percent annually, paying 50 times today's earnings might be perfectly reasonable. Those earnings will double in three years and double again in six. The PE collapses on its own as profits catch up to the price.
This is why fast-growing consumer tech, pharma, and IT companies often trade at higher multiples than, say, a PSU bank. Investors are paying for future earnings, not just the current year's number.
When PE is useless
PE breaks down the moment earnings turn negative or approach zero. Loss-making companies, businesses in a cyclical trough, or companies undergoing restructuring all produce PE numbers that mean nothing. Indigo Airlines posted a massive loss during Covid. Paytm burned cash for years after its 2021 IPO. Using PE to evaluate either of those in bad years would tell you nothing useful.
The other failure mode is when one-time items distort earnings. A company might sell a factory and post extraordinary profit for one year, making the PE look cheap. Or it might take a large write-down and look expensive. Always check whether the earnings number reflects the actual business or just an accounting event.
Forward PE vs trailing PE
The standard PE uses the last twelve months of earnings. Forward PE uses analyst estimates of the next twelve months. Neither is perfectly accurate, but forward PE is often more useful for fast-growing companies because it reflects where the business is headed.
Nifty 50 itself trades at a PE. Historically, the index has averaged around 20 to 22 times trailing earnings. When it crosses 25, markets are pricing in optimism. When it falls below 15, fear is doing the pricing. Neither automatically means buy or sell, but it gives context.
The PE ratio is one lens. A company with a low PE and shrinking profits is not a bargain. A company with a high PE and accelerating growth might be the best investment available. The number only makes sense alongside the growth story behind it.