A glossary of market measures
Each term is defined in a sentence or two, given its latest S&P 500 reading where one exists, and linked to the chart that tracks it.
AIAE (Aggregate Investor Allocation to Equities)
The share of investors' financial assets held in stocks: the market value of US equities divided by that value plus the total debt of US borrowers, which stands in for the bonds and cash investors could hold instead. High readings have been followed by low ten-year returns.
In the data: 51.4% in Q2 2026 (quarterly); average since 1945: 32.0%.
Chart: AIAE: Aggregate Investor Allocation to Equities · Read: Shiller PE Today: Is the U.S. Stock Market Overvalued?
Shiller CAPE (cyclically adjusted P/E)
The S&P 500's price divided by its average inflation-adjusted earnings over the previous ten years. Averaging a decade of earnings smooths out booms and recessions, so the ratio tracks valuation across the business cycle.
In the data: 41.4 on October 2, 2026; average since 1871: 17.6.
Chart: Shiller CAPE: Cycle-Smoothed Price-to-Earnings Ratio · Read: Shiller PE Today: Is the U.S. Stock Market Overvalued?
Forward P/E
Price divided by analysts' consensus estimate of earnings over the next twelve months. Because it looks ahead, it sits below the trailing P/E when earnings are expected to grow.
In the data: 19.1 on October 7, 2026 (twelve-month forward consensus).
Chart: S&P 500 Trailing vs. Forward P/E Multiples · Read: Shiller PE Today: Is the U.S. Stock Market Overvalued?
Trailing P/E
Price divided by the earnings companies actually reported over the past twelve months.
In the data: 27.2 on October 8, 2026, weighted by market value across current members.
Chart: S&P 500 Trailing vs. Forward P/E Multiples · Chart: Shiller CAPE: Cycle-Smoothed Price-to-Earnings Ratio · Read: Shiller PE Today: Is the U.S. Stock Market Overvalued?
Total return vs price return
Price return counts only the change in the index level. Total return also counts dividends, assumed reinvested. The gap compounds: an index's long-run total return is far larger than its price change.
In the data: Average calendar year since 1928: +11.9% total return, +8.1% price return.
Chart: A Century of Calendar-Year Returns · Chart: Total Return Architecture: Price Gains, Dividends, and Buybacks · Read: S&P 500 Annual Returns by Year: Complete Table 1928–2026
Annualized return (CAGR)
The constant yearly rate that turns a starting value into an ending value: (end ÷ start)^(1 ÷ years) − 1. When yearly returns swing, it is lower than their simple average.
In the data: S&P 500 price index from January 1928 to October 2, 2026: 6.4% a year.
Chart: Annualized Return Matrix: Pick Any Buy and Sell Year · Chart: Five-Year Rolling Horizons: Annualized Return Distribution · Return calculator · Read: Will the S&P 500 Be Up in 10 Years? Every Rolling Window Since 1928
Drawdown
The fall from the highest close so far to a later low, in percent. A drawdown ends when the index closes above the old record again.
In the data: 73 declines of 5% or more from a record close since 1928; median −8.2%.
Chart: Historical Drawdowns: The Morphology of Market Declines · Read: S&P 500 Maximum Drawdowns: The Complete Bear Market Register Since 1929
Correction
A decline of 10% to 20% from a record close: deeper than a dip, shallower than a bear market.
In the data: 14 since 1928, counted on daily closes.
Chart: Historical Drawdowns: The Morphology of Market Declines · Read: S&P 500 Maximum Drawdowns: The Complete Bear Market Register Since 1929
Bear market
A decline of 20% or more from a record close.
In the data: 12 since 1929; the deepest fell 86.2%.
Chart: Historical Drawdowns: The Morphology of Market Declines · All bear markets · Read: S&P 500 Maximum Drawdowns: The Complete Bear Market Register Since 1929
Intra-year decline
The largest peak-to-trough drop inside a single calendar year, measured on daily closes. A year can end well up and still have contained a deep one.
In the data: Average since 1928: −16.2% within the year, while the average year ended +8.1%.
Chart: Maximum Intra-Year Drop vs. Full-Year Return · Read: Stock Market Crash History: Every Major U.S. Crash Since 1929
VIX
The Cboe Volatility Index: the volatility of the S&P 500 over the next 30 days implied by option prices, in annualized percent. It rises when investors pay up for protection.
In the data: 15.1 on October 7, 2026; average since 1990: 19.4.
Chart: Cboe Volatility Index (VIX): Pricing Market Tail Risk · Read: The VIX Explained: What the Fear Index Measures and Every Spike Since 1990
Market breadth
The share of index members trading above a moving average of their own price, here the 200-day. An index rising while breadth falls is being carried by fewer stocks.
In the data: 47.0% of S&P 500 members above their 200-day average on October 7, 2026.
Chart: Bull-Market Breadth: Participation Above Moving Averages