Equity Premium

The equity premium (also called the equity risk premium or ERP) is the additional return investors earn by holding stocks instead of risk-free government bonds. It represents the compensation the market demands for accepting the uncertainty and volatility of equity ownership. Historically, the U.S. equity premium has averaged roughly 4-6% annually — meaning stocks have returned about 4-6 percentage points more per year than Treasury bonds over long periods.

The equity premium is arguably the most important number in investing because it drives virtually every major financial decision. It determines whether stocks are worth their risk, how much of your portfolio should be in equities versus bonds, the discount rate used in company valuations (DCF models), pension fund assumptions, and even Social Security's long-term projections. A higher equity premium makes stocks more attractive; a lower one tilts the balance toward bonds and alternative investments.

The "equity premium puzzle," identified by economists Mehra and Prescott in 1985, notes that the historical premium is far larger than standard economic models would predict. Given the actual volatility of stocks, rational models suggest the premium should be about 0.5-1% — yet the observed premium is 4-6%. This means either investors are far more risk-averse than models assume, or historical returns included unsustainable luck (the U.S. experiencing the best century of any stock market in history), or there are behavioral biases (like loss aversion and myopic loss aversion) that drive investors to demand excessive compensation for volatility.

For practical investing, the forward-looking equity premium matters more than the historical one. Current estimates for the expected equity premium range from 3-5%, depending on methodology. When stock valuations are high (high P/E ratios), the expected future premium tends to be lower — you're paying more for the same future earnings. When valuations are low (like during crashes), the expected premium is higher. Understanding this helps investors make informed asset allocation decisions rather than simply extrapolating past returns into the future.