The CAPE ratio is one of the most cited valuation tools in global equity markets, and in May 2026 it is flashing again. The S&P 500 Shiller PE sits near 41.6, more than twice the long-run average of roughly 17.3.
That reading is the second highest in over 140 years of US market history. Only the December 1999 peak of 44.19 was richer.
For long-horizon investors, the question is not whether the number looks high. It is what a high CAPE has historically meant for the next decade of returns, and how to weigh that signal against other valuation lenses.
What the CAPE Ratio Actually Measures
The cyclically adjusted price-to-earnings ratio was introduced in 1988 by Yale economist Robert Shiller and John Campbell. It divides the current S&P 500 price by the average of the last 10 years of inflation-adjusted earnings.
The 10-year window is the point of the design. A single year of earnings can be distorted by a recession, a tax change, or a one-time write-down. Averaging a decade smooths the business cycle and gives a steadier denominator.
According to multpl.com, which publishes Shiller's official data series, the May 2026 reading sits around 41.6. The long-term mean since 1881 is approximately 17.3.
How Today's Reading Compares to History
A CAPE above 40 has only been recorded twice. The first was at the dot-com peak in December 1999, when the ratio hit 44.19 before the index lost roughly half its value over the following two and a half years.
The second is now. The current reading puts the S&P 500 in rarefied valuation territory, well above the 1929 pre-crash level near 32 and far above the 2007 pre-financial-crisis peak near 27.
Context matters. Today's index is heavier in software and large-cap technology, where reported earnings tend to be more durable than the cyclical industrials that dominated earlier eras. Some analysts argue that justifies a structurally higher CAPE.
Others, including Shiller himself, counter that elevated readings have historically been a poor reason to assume the rules have changed.
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What High CAPE Has Meant for Forward Returns
The academic relationship between starting CAPE and subsequent 10-year real returns is one of the more durable findings in finance. According to research summarized by Morningstar, forward 10-year real returns on the S&P 500 have dropped almost monotonically as starting CAPE has risen.
When the CAPE was below 9.6, the next 10 years delivered average real returns of about 9.8 percent annually. When the CAPE was above 25, forward 10-year real returns averaged in the low single digits or worse.
The relationship is not deterministic. Even at elevated starting valuations, individual 10-year windows have produced a wide range of outcomes. Earnings growth, inflation paths, and Federal Reserve policy all influence the path the index actually takes.
What CAPE does suggest, with reasonable statistical confidence, is that the central estimate for the next decade is materially lower than the long-run S&P 500 average of roughly 7 percent real.
Using CAPE Alongside Earnings Yield and Risk Premium
CAPE works best when treated as one input rather than a standalone verdict. Two companion measures help round out the picture.
The first is the CAPE earnings yield, calculated as 1 divided by the CAPE ratio. At a CAPE of 41.6, the earnings yield is about 2.4 percent. That is the real annual yield the index would deliver if cyclically adjusted earnings simply held steady.
The second is the equity risk premium, which compares the earnings yield against the real yield on long-dated Treasuries. When real Treasury yields are high, even a modest earnings yield offers less compensation for taking equity risk. When real yields are low, a smaller earnings yield can still be acceptable.
Together, these three lenses give you a more honest valuation picture than any single number. The CAPE tells you where the index sits relative to its own history. The earnings yield tells you what you are buying in absolute terms. The risk premium tells you whether the trade-off versus bonds still makes sense.
Conclusion
In May 2026, the Shiller CAPE ratio is signaling that US large-cap equities are historically expensive. The reading near 41.6 is the second highest on record and well above the long-run mean of 17.3.
That does not predict a crash, and high CAPE readings have persisted for years before mean-reverting. What the data does support is a more sober base case for the next decade of S&P 500 returns, and a stronger argument for diversification across geographies, asset classes, and time.
FAQ
Q: What is considered a high CAPE ratio?
A: The long-run average is roughly 17. Readings above 25 are considered elevated, and anything above 30 is historically rare. The May 2026 reading near 41.6 is the second highest in over 140 years.
Q: Has a high CAPE always meant a market crash is coming?
A: No. CAPE has stayed elevated for years at a time. It is a better predictor of long-horizon returns than of short-term timing. The 1990s ran with high CAPE for most of the decade before the dot-com correction.
Q: Why is the CAPE so high in 2026?
A: A combination of strong large-cap tech earnings, sustained margin expansion, and investor willingness to pay up for index exposure. Whether those drivers are durable or cyclical is the live debate among investors.
