The S&P 500's Shiller P/E, or CAPE ratio, sits near 41 — the second-most expensive market in history, trailing only the dot-com peak of 44. The reading arrives just as September opens, historically the S&P 500's weakest month, layering a seasonal pattern on top of a stretch of investor worries.
Wall Street's most reliable valuation gauge has been flashing a warning for months, and history offers a mixed read on what typically comes next.
A valuation metric flashing a warning
The CAPE averages the S&P 500's last decade of inflation-adjusted earnings, smoothing over one-off swings from recessions or profit surges to give a clearer read on how expensive stocks look. Over 155 years, the average CAPE reading sits at about 18, well below where the market trades now. A stock valuation running this far above its historical average has typically preceded weaker long-term returns, though the metric doesn't predict whether or when a downturn follows — a high CAPE does not cause a crash, it simply signals stocks look historically expensive.
September's bad reputation meets real uncertainty
September has historically delivered negative or weaker returns with enough consistency that traders call it "the September Effect." This year that seasonal pattern lands alongside sticky inflation, rising energy prices, hawkish signals from central bankers, high yields on Treasury bonds, a trade war between the U.S. and Canada, an actual war between the U.S. and Iran, ballooning national debt, and continued fears of an AI bubble. Still, the picture isn't only negative: S&P 500 companies have posted soaring profits, the U.S. economy keeps growing steadily, and the market has broadened beyond a handful of megacap leaders.
What investors are being told to do
The advice circulating alongside the data is to avoid overreacting. Panicking, trying to time the market, or selling good companies indiscriminately could do more damage than a downturn itself. Instead, the recommendation is to stay invested in companies worth believing in regardless of near-term swings in the broader market.
Sources: Motley Fool via Yahoo Finance, The Motley Fool
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