What History Reveals About a Potential Stock Market Crash in 2026

The S&P 500 has delivered strong gains over the past several years. Artificial intelligence remains a dominant investment theme, and stock valuations have climbed well above historical averages. Whenever markets reach these levels, discussions about an impending crash tend to follow -- and with good reason.

Indeed, history offers a useful perspective.

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The CAPE ratio

One of the most widely followed valuation measures is the Shiller P/E CAPE ratio, which compares stock prices to average inflation-adjusted earnings over the previous 10 years. Historically, elevated CAPE ratios have been associated with lower long-term returns and, in some cases, major market corrections. And today, the CAPE ratio remains elevated.

That doesn't mean a crash is imminent, though.

History shows that expensive markets can remain expensive for years. In fact, the CAPE ratio first moved above its long-term average in the mid-1990s, yet the market continued rising for several more years before the dot-com bubble eventually burst.

Market concentration

Another indicator attracting attention is market concentration. A relatively small group of technology companies now accounts for an unusually large share of the S&P 500's value.

Nvidia (NASDAQ: NVDA), Microsoft (NASDAQ: MSFT), Apple (NASDAQ: AAPL), Amazon (NASDAQ: AMZN), Alphabet (NASDAQ: GOOG), Meta (NASDAQ: META), and Broadcom (NASDAQ: AVGO) have become so large that their combined market value exceeds that of entire sectors of the economy. And when these stocks move higher, they can pull the broader market with them. The reverse is also true, of course. If investor sentiment shifts, weakness in just a handful of names can have a meaningful impact on major indexes.

Similar periods of concentration have occurred before. During the "Nifty Fifty" era of the early 1970s -- when roughly 50 big stocks were bought at any price -- and the internet boom of the late 1990s, investors crowded into a handful of dominant companies. In both cases, the broader market eventually experienced significant declines.

Of course, there are important differences between today's environment and past bubbles. Many of today's largest companies are highly profitable, generate substantial cash flow, and hold strong balance sheets. Unlike many internet companies during the dot-com era, these businesses are producing real earnings and returning capital to shareholders.

The economy also remains relatively stable. Unemployment is low, corporate profits remain healthy, and consumer spending has held up despite higher interest rates. But that doesn't eliminate risk.

Historically speaking

History tells us that market corrections are a normal part of investing. As The Motley Fool notes: "The stock market loses 10% of its value about once per year on average. Declines of 20% tend to happen every four or five years. Even bigger stock market crashes, with the major indexes losing 30% of their worth, occur at roughly 10-year intervals."

What history does not reveal is exactly when the next major downturn will occur. Analysts and experts have spent years predicting crashes that never arrived. Others assumed bull markets would continue indefinitely, only to be caught off guard by sudden reversals.

What history tells us is not that a crash is coming in 2026. It's that markets eventually correct, valuations do matter, and risk becomes palpable when optimism is widespread. To be sure, history has generally rewarded discipline over prediction. Maintaining a diversified portfolio and focusing on business fundamentals has certainly proven to be a more reliable strategy than trying to forecast the exact timing of the next market crash.

Jeff Siegel has no position in any of the stocks mentioned. The Motley Fool has positions in and recommends Alphabet, Amazon, Apple, Broadcom, Meta Platforms, Microsoft, and Nvidia. The Motley Fool has a disclosure policy.