What Is the P/E Ratio?

How to Calculate and Read a P/E Ratio

P/E = Stock Price ÷ Earnings Per Share (EPS). If a stock trades at $100 and earned $5 per share over the last 12 months, its P/E is 20. There are two common versions:

• Trailing P/E — uses actual earnings from the past 12 months. More reliable, based on real results
• Forward P/E — uses analyst estimates for the next 12 months. Reflects growth expectations, but estimates can be wrong
• As of 2024, the S&P 500's long-run average P/E sits around 15–18. Above 25 is elevated; above 40 is speculative territory

What Counts as Cheap or Expensive?

P/E ratios vary enormously by sector. Technology growth companies routinely trade at 30–60x earnings because investors are paying for future growth. Mature consumer staples like Coca-Cola or Procter & Gamble typically trade at 20–28x. Banks and energy companies often trade at 8–14x. A low P/E is not automatically a bargain — it may signal that earnings are about to decline, the business is in a structural decline, or the market perceives elevated risk.

When the P/E Ratio Misleads You

The P/E ratio has significant blind spots. It ignores debt entirely — a company can look cheap by P/E while carrying crushing liabilities. It becomes meaningless when earnings are negative (loss-making companies have no P/E). It can be distorted by one-time charges or tax benefits that inflate or deflate reported earnings. Growth companies are almost always "expensive" by P/E but may still be excellent investments if growth materialises. Use P/E alongside other metrics: P/S ratio, EV/EBITDA, free cash flow yield.

P/E in the Context of Risk

High P/E stocks carry a specific kind of risk: valuation compression. If earnings disappoint even slightly, a stock at 50x earnings can fall 30–40% simply from the multiple contracting back to 30x — even if earnings themselves are fine. This is why GlobalTrack tracks valuation risk as one of its 8 risk dimensions. During rising interest rate environments, high-P/E growth stocks tend to de-rate faster than the broader market.