The S&P 500's Shiller P/E Ratio stood at 42.37 on Aug. 10, within reach of the 44.19 all-time high set during the dot-com bubble in December 1999. History shows the metric has topped 30 during a bull market only six times since 1871, and the previous five instances were all followed by declines of 20% to 89%. Even so, long-run data show every rolling 20-year period since 1900 has produced a positive return.
Valuations flash the market's most glaring warning sign
The Dow Jones Industrial Average, S&P 500, and Nasdaq Composite had climbed 12.3%, 13.3%, and 14.5% year-to-date, respectively, as of the close on Aug. 10, extending a bull run fueled by heavy AI infrastructure spending and corporate earnings that beat Wall Street's projections. But stock valuations now represent the most glaring red flag for the market, ahead of margin debt and inflation.
Founded on average inflation-adjusted earnings from the prior decade, the Shiller P/E Ratio, or CAPE Ratio, has averaged 17.4 since it was backtested to January 1871. It stood at 42.37 as of Aug. 10, roughly 144% above that long-term average. The metric has been higher only once before: it peaked at 44.19 in December 1999, in the run-up to the dot-com crash. The current bull market has so far topped out at a CAPE Ratio of 42.84 on June 1.
Since 1871, the S&P 500's Shiller P/E Ratio has crossed above 30 during a continuous bull market six times, including now. Each of the previous five occurrences was eventually followed by declines in the Dow, S&P 500, or Nasdaq Composite ranging from 20% to 89%. The valuation metric cannot pinpoint the timing or trigger of a downturn, but it shows premium multiples rarely hold for long.
Long-term data still favor patient investors
Historically, downturns are routine: the S&P 500 has suffered a double-digit percentage decline roughly once a year on average. Yet cycles aren't linear. Bespoke Investment Group data covering every S&P 500 bull and bear market since September 1929 found the average bear-market trough arrives after 286 calendar days, and no bear market has ever lasted beyond 630 days.
By contrast, the average S&P 500 bull market has run about 1,023 calendar days, roughly 3.6 times longer than the average bear market, and 14 of the 27 bull markets on record have outlasted the longest bear market. Crestmont Research's analysis of 107 rolling 20-year windows dating to 1900 found that every single one produced a positive annualized total return, including dividends.
The historical pattern doesn't rule out a sharp pullback from today's stretched valuations. But it does suggest that investors who hold through any downturn have, over the past century, ended up on the right side of the trade.
Source: The Motley Fool
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