The Stock Market Is Flashing a Rare Warning Signal. Here's What History Says Happens Next.
Key Points
The total U.S. stock market value-to-GDP ratio is known as the "Buffett indicator."
It just reached 2x its standard deviation, a level that has historically preceded a market downturn.
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If you want to know where the stock market is heading, you're not alone.
While nobody knows with certainty where the S&P 500 (SNPINDEX: ^GSPC) will go on any given day, week, month, or even year, there are certain indicators with a strong historical track record of preceding market downturns. And unfortunately, one of them just started flashing bright red.
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Image source: Getty Images.
That indicator is the US Stock Market Total Value-to-GDP ratio, also known as the "Buffett indicator." It's named after legendary investor Warren Buffett, the board chairman of Berkshire Hathaway. Buffett once called the ratio "the best single measure of where valuations stand at any given moment."
The Buffett indicator's historical trend line has gradually increased over time, from below 50% in 1950 to about 134% today. So to make historical comparisons, many analysts look at its standard deviation (SD) lines.
I won't get into the complicated math (but if you're interested, one SD is the square root of the total variance of all the data points from the trendline), so here's the big takeaway: Historically, when the Buffett indicator hits two SDs above its trendline, a big market downturn has occurred.
Between 1950 and 2025, the Buffett indicator only hit that threshold three times:
- Just before the stock market crash of 1968,
- Right before the dot-com bubble burst in 2000,
- Immediately prior to the post-pandemic 2022 bear market.
In April and May 2026, however, the Buffett indicator jumped to well above the +2SD threshold, its highest level in history by a significant margin.
Image source: Getty Images.
Now, this doesn't prove that a market downturn is imminent, but it's certainly a flashing warning signal from the market that stock valuations are extraordinarily high right now.
Investors should proceed with extreme caution and be prepared to stomach volatility in the near future. However, resisting the urge to panic sell is also important: History shows that riding out periods of market turbulence is usually the best strategy.
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John Bromels has positions in Berkshire Hathaway. The Motley Fool has positions in and recommends Berkshire Hathaway. The Motley Fool has a disclosure policy.
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