I propose and test a simple model of the equity premium implied by the prices of options on the stock market. The model assumes that markets for the stock index and its options are frictionless and complete to extract as much information as possible from their prices. Its forecasts of the equity premium are more accurate than those in prior work, especially when arbitrage costs are low. It offers new economic insights into why the premium varies, including why it increased for many years after the 2008 crisis. The model also provides a unified explanation of risk premiums for variance and higher-order moments of market returns.