Price-to-Earnings Ratio (P/E)

The price-to-earnings ratio, or P/E, divides a company's share price by its earnings per share: a $100 stock earning $5 a year trades at a P/E of 20, or twenty years of current profits. It is the most quoted valuation ratio in the market, and it answers a different question than price alone: not what a share costs, but what it costs per dollar of earnings. The inverse is the earnings yield, a P/E of 20 being a 5% earnings yield.

Two versions are quoted. The trailing P/E divides by the last twelve months of reported earnings, which is factual and always late. The forward P/E divides by forecast earnings, which is timely and always a forecast. The S&P 500 has traded at an average P/E near 16 to 17 over the past century, with the 2025 index running in the mid-20s, a premium the market paid for growth and margin stability.

The ratio is one division, and the denominator is the one with the personality. When earnings grow and price holds, the P/E falls and the stock gets cheaper on the same price. When earnings collapse and price holds, the P/E rises while the business worsens. Price tags the expectation; earnings deliver the reality, and the ratio is the handshake between them.

Comparison is the discipline. A P/E means little in isolation and much against three benchmarks: the company's own history, its sector, and the index. Banks have traded near 10 to 12 for structural reasons; software companies near 30 or more for growth and margin reasons; a bank at 11 is normal, and a bank at 11 in a crisis is a warning. The Shiller CAPE smooths earnings over ten years to strip the cycle out of the denominator.

The earnings yield makes the ratio comparable to everything else. A P/E of 25 is a 4% earnings yield, directly comparable to a 4.5% high-yield savings rate; the stock only wins if earnings grow or the multiple holds. That is the entire valuation question compressed into one division.

P/E is the number that separates paying for a business from paying for a story. It will not tell you what to buy, but it will tell you what the crowd currently believes, and the crowd is frequently overpaying or underpaying in ways that take years to resolve.

I watched a colleague named Brent (yes, that Brent) buy a P/E-of-6 industrial he called cheap, without asking why the market priced six years of earnings. The answer was a shrinking order book: earnings halved over the next two years, and the cheap multiple was repriced on smaller earnings. A low P/E is a hypothesis, never a verdict.

The highest-leverage thing most Americans can do is hold a diversified index fund where the average P/E is one input to a decade, and check the index multiple only to calibrate expectations, not to time exits. Screen individual holdings with the P/E ratio calculator and check the earnings input with the EPS calculator.