S P 500 Historical PE Average

S&P 500 Historical Average P/E

You get the S&P 500's price-to-earnings ratio from P/E = Index Price / Aggregate EPS, with the index covering the 500 largest U.S. companies by market capitalization. Over the long haul the median lands around 15–16x. The extremes range from 6–8x in the early 1980s, when inflation was high and rates ran into double digits, up to 25–30x during the dotcom bubble and again in the COVID-19 stimulus cycle.

Robert Shiller gave us the Cyclically Adjusted Price-Earnings ratio (CAPE or Shiller P/E), which averages 10 years of inflation-adjusted earnings to iron out the business cycle. His 2000 book "Irrational Exuberance" is what put CAPE on the map as a long-horizon valuation gauge. If you want to own the index itself, the usual vehicles are SPY (SPDR), IVV (iShares Core) and VOO (Vanguard).

Applications

A historical mean P/E gives tactical allocation a yardstick. When the reading sits well above the median it can point to overvaluation and dimmer 10-year prospects, and historically the cheap multiples have tended to come before forward returns that beat the average. The same metric feeds into equity risk premium models and allocation frameworks at shops like GMO and Research Affiliates.

FAQ

Trailing vs forward P/E? Trailing leans on the last 12 months of reported earnings. Forward uses analysts’ estimates for the coming 12 months, and it usually reads lower during expansions and higher as a recession approaches.

Why does CAPE differ from standard P/E? CAPE divides price by a 10-year average of real earnings, which damps down the cyclical swings. It usually comes out higher than trailing P/E, since the average pulls in older earnings at lower nominal levels.

Is P/E a good market-timing tool? Not over short horizons. Valuation lines up reasonably well with 7–10 year forward returns, but it says little about the next 12 months, where sentiment and liquidity call the shots.