S&P 500's Shiller P/E Ratio Nears 150-Year Record High — What History Says Happens Next

Stock Market Valuations Approach Territory Unseen in Over a Century

Wall Street has delivered another remarkable run for investors in 2026, with the Dow Jones Industrial Average (^DJI), S&P 500 (^GSPC), and Nasdaq Composite (^IXIC) all reaching fresh all-time highs earlier this month. But lurking beneath the celebratory headlines is a valuation signal that has preceded some of the most severe market downturns in modern history — and it's now approaching record-breaking levels not seen in over 150 years.

The CAPE Ratio: A Time-Tested Warning Signal

Among the various tools analysts use to gauge market valuation, few carry the historical weight of the Shiller Price-to-Earnings Ratio, also known as the Cyclically Adjusted P/E Ratio or CAPE Ratio. Unlike the traditional P/E ratio, which compares a stock's price to just the past 12 months of earnings, the Shiller P/E incorporates inflation-adjusted earnings averaged over the prior decade. This longer time horizon smooths out the distortions caused by economic cycles and recessions, giving a more stable view of whether the broader market is expensive or cheap relative to history.

The metric has been back-tested to January 1871 — more than 155 years of data — and over that entire span, the S&P 500's CAPE Ratio has averaged 17.39 through June 15, 2026.

When the major indexes surged to new highs earlier this month, the Shiller P/E climbed to 42.84 — a fresh peak for the current bull market and a level that has only been reached twice before in recorded history.

Only Three Times in 155 Years

The data paints a sobering picture. The CAPE Ratio has exceeded 40 during a continuous bull market on just three occasions since the 1870s, including the present moment.

The first comparison point is particularly recent: in early January 2022, the Shiller P/E briefly crossed above 40 — but only for a matter of days. What followed was a nine-month bear market that erased roughly 25% of the S&P 500's value.

The second — and more dramatic — precedent came in December 1999, when the CAPE Ratio reached its all-time peak of 44.19. That reading arrived just months before the dot-com bubble began deflating, ultimately cutting the S&P 500 nearly in half and slashing the Nasdaq Composite by a staggering 78%.

Now, with the current reading at 42.84, analysts note that the enthusiasm surrounding artificial intelligence, quantum computing, IPO activity, and record share buybacks could push valuations even higher — potentially eclipsing that 1999 record.

Context Matters: The Bull vs. Bear Market Asymmetry

While these historical comparisons raise legitimate concerns, perspective remains a critical tool for long-term investors. Market data consistently shows a stark imbalance between how long bull and bear markets tend to last.

Research from Bespoke Investment Group, updated recently on social media platform X, analyzed every S&P 500 bull and bear market since September 1929. Their findings indicate that the average bear market lasted just 286 calendar days — roughly 9.5 months — with no bear market exceeding 630 calendar days in that entire 96-year period.

Bull markets, by contrast, averaged 1,023 calendar days in length. More notably, 14 out of 27 S&P 500 bull markets lasted longer than the lengthiest bear market on record.

Adding further long-term context, analysts at Crestmont Research examined rolling 20-year total returns for the S&P 500 — including dividends — going all the way back to 1900. Their analysis generated 107 separate 20-year rolling periods, from 1900–1919 through 2006–2025.

The result: every single one of those 107 periods produced a positive annualized total return. Recessions, depressions, wars, pandemics, and even historically stretched valuations ultimately failed to prevent the index from generating gains over any 20-year window.

What to Watch Going Forward

The CAPE Ratio cannot pinpoint market tops with precision — no single metric can. But the data suggests that elevated valuations of this magnitude have consistently preceded significant drawdowns. Whether the current AI-driven enthusiasm can sustain premium valuations beyond the 1999 record of 44.19 remains an open question.

For investors, the key variables to monitor include the trajectory of corporate earnings relative to price levels, Federal Reserve policy decisions, inflation trends, and whether the momentum behind AI and technology spending continues to justify current multiples. Consumer sentiment data — which hit an all-time low on the University of Michigan's index in May — and rising margin debt levels are also signals analysts are watching closely.

History does not repeat itself with mechanical precision, but the weight of 155 years of valuation data suggests the current environment warrants careful attention from market participants at every level.