S&P 500 Trailing Operating P/E vs. Robert Shiller CAPE Ratio
Audited 12-Month Operating Corporate Earnings Multiples, 10-Year Inflation-Adjusted Real Valuations, and Equity Risk Premium Dynamics (1990–2026)
The S&P 500 trades at a 25.84x trailing 12-month operating P/E and a 40.23x Robert Shiller CAPE ratio (sitting at the 94.6th historical percentile since 1990). While trailing P/E captures the latest four quarters of audited corporate earnings ($295.39/share), Shiller's CAPE smooths out cyclical volatility by dividing the real index price by the 10-year moving average of inflation-adjusted real earnings. Historically, CAPE readings above 35x have occurred exclusively during the 1999–2000 Dot-Com bubble peak (44.2x), the 2021 zero-rate monetary stimulus expansion (38.6x), and the 2024–2026 generative AI infrastructure surge.
Read Master Reference Guide: Pillar VI: Equities and Valuation — Cost of Capital, Multiples & Risk Premia →Historical Macro Cycle Benchmarks & Inflection Points
Pre-rendered empirical time-series data table for search engine verification and cycle benchmarking.
| Macro Cycle Phase | S&P 500 Trailing 12M P/E | Robert Shiller CAPE Ratio | Valuation Cycle Phase | Implied Macro Regime |
|---|---|---|---|---|
| March 2000 (Dot-Com Bubble Peak) | 29.50x | 44.20x | Extreme Speculative Euphoria | Historical All-Time Peak CAPE |
| October 2002 (Tech Bust Trough) | 16.00x | 21.50x | Cyclical De-Rating | P/E Compression Post-Recession |
| October 2007 (Housing Boom Peak) | 17.50x | 27.50x | Credit Expansion Equilibrium | Moderate Multiple Before Banking Collapse |
| March 2009 (GFC Liquidity Crash Trough) | 13.00x | 13.30x | Extreme Distress & Fire-Sale | Historic Generational Valuation Trough |
| December 2018 (Fed Quantitative Tightening) | 17.20x | 28.30x | Fed Tightening Drag | Multiple De-Rating on Real Rate Surge |
| March 2020 (Pandemic Crash Trough) | 18.00x | 24.80x | Deflationary Shock | Instantaneous Crash Before Fiscal Stimulus |
| December 2021 (Peak Stimulus & Zero Rates) | 26.50x | 38.60x | Zero-Rate Liquidity Peak | Post-War Historical Multiple Extreme |
| October 2022 (Fed 500bps Rate Hikes) | 18.20x | 27.10x | Rapid P/E Multiple De-Rating | Equity Risk Premium Compression |
| September 2026 (Current Live Baseline) | 25.84x | 40.58x | Substantially Elevated Multiple | AI Infrastructure & Tech Multiple Expansion |
1. The Architecture of S&P 500 Trailing Operating P/E
The Trailing 12-Month Operating Price-to-Earnings (P/E) multiple measures the current market price of the S&P 500 index relative to the sum of the last four quarters of audited operating corporate earnings per share (EPS). Unlike speculative forward estimates generated by sell-side brokerage analysts, operating earnings reflect audited financial filings compiled by S&P Dow Jones Indices. Operating earnings exclude unusual non-operating items such as goodwill impairment charges, asset write-downs, and litigation settlements, providing the pure corporate earnings power generated from core business operations.
2. Robert Shiller's Cyclically Adjusted P/E (CAPE / P/E 10)
Introduced by Nobel laureate Robert J. Shiller and John Y. Campbell, the Cyclically Adjusted Price-Earnings (CAPE) ratio addresses a critical vulnerability in traditional trailing multiples: the earnings trough distortion. During recessions (such as 2008–2009), trailing one-year earnings collapse dramatically, causing traditional P/E multiples to spike artificially to 100x+ at the exact moment equities are generationally cheap. To eliminate business cycle noise, CAPE divides the real (inflation-adjusted) price of the S&P 500 by the 10-year moving average of real corporate earnings:
$$\text{CAPE}_t = \frac{P_t}{\frac{1}{10} \sum_{k=1}^{120} \text{Real EPS}_{t-k}}$$
By smoothing corporate earnings over an entire decade, CAPE captures both peak expansion years and recessionary troughs, revealing whether current equity valuations reflect structural multiple expansion or temporary earnings anomalies.
3. Historical Valuation Regimes & The Equity Risk Premium (ERP)
Over the full empirical period from 1881 to 2026, the historical median CAPE ratio sits at approximately 16.5x to 17.5x, while the post-1990 modern median is 26.4x. Sustained CAPE readings above 35x have occurred in only three distinct market eras: the 1999–2000 Dot-Com bubble peak (44.2x), the 2021 zero-rate fiscal liquidity expansion (38.6x), and the 2024–2026 generative AI infrastructure surge (40.6x). In an environment where the 10-Year Treasury yield trades near 4.25%–4.50%, an equity earnings yield of 3.87% (1 / 25.84) results in a flat to negative Equity Risk Premium (ERP), signaling that investors are demanding virtually zero excess spread to hold equities over risk-free sovereign debt.