A Repeat Of ‘Black Monday’ Would Send The S&P 500 Down More Than 1,500 Points And Wipe Out More Than $13 Trillion In Stock Market Value
Thirty-nine years after a single October Monday vaporized trillions and paralyzed markets worldwide, analysts are drawing uncomfortable parallels between 1987 and today's AI-fueled rally, and the math behind a repeat scenario is sobering.
The benchmark S&P 500 is still up 11.9% this year, but Wall Street marks Monday, Oct. 19, 2026, the 39th anniversary of the 1987 crash, after a rough week.
On that day in 1987, the Dow Jones Industrial Average suffered its largest one-day percentage drop ever, a 22.6% collapse. But applying Black Monday‘s 20.47% S&P 500 decline to Friday’s close would erase about 1,568 points by our arithmetic, leaving the index near 6,092. The Dow’s 22.61% drop would remove about 11,750 points, leaving it near 40,245.
This is simple arithmetic on Friday’s closes and is not meant as a prediction.
In dollars, the same S&P 500 decline applied to the index’s $68.45 trillion market cap at the end of the third quarter, equals about $14.0 trillion.
Friday rattled investors, the S&P 500 fell 1.1% to 7,659.44, the Dow slid 0.3% to 52,002.41 and the technology-packed Nasdaq Composite tumbled 2.1% to 26,140.03. The S&P 500 and Nasdaq logged their worst week since June, led by chip stock. The Dow and Nasdaq remain up 8.2% and 12.5% this year.
How Black Monday, October 19, 1987, Unfolded
The Dow fell 3.81% on Oct. 14, 2.39% on Oct. 15 and 4.6% on Oct. 16. On Oct. 19, it opened at 2,246.74 and closed at 1,738.74, a 508-point plunge. The S&P 500 sank 20.47%, the Wilshire 5000 dropped 18% and estimated worldwide losses reached $1.71 trillion. Systems struggled: 195 of 2,257 NYSE-listed stocks faced delays or halts, and 95 S&P 500 stocks opened late while futures opened on time.
What Lit the Fuse in 1987
Possible triggers included a House bill to curb tax benefits for mergers and leveraged buyouts and a higher-than-expected trade deficit released Oct. 14. Many saw stocks as overvalued, while trade and budget deficits, rising interest rates and a falling dollar added to concern. Portfolio insurance (computer-driven selling of index futures), index arbitrage through program trading, weekend mutual fund redemptions and early selling ahead of the expected Monday drop amplified the rout. The 1988 Brady Report found margin calls ran about ten times their average size and judged portfolio insurance a possible contributing factor rather than the initial trigger.
How the Fed Stopped the Bleeding
On Oct. 20, Fed Chairman Alan Greenspan said the Fed “affirmed today its readiness to serve as a source of liquidity.” It injected $17 billion that day, and the federal funds rate fell about half a percentage point. The S&P 500 bottomed at 230.30 in November 1987, down 31.6% from its Aug. 25 high of 336.77, and regained that high on July 26, 1989.
Why Circuit Breakers Change the Math
The NYSE adopted trading curbs in 1988, and regulators later created market-wide circuit breakers, used during the 2020 crash. Under the SEC’s investor guidance, a single-day S&P 500 decline of 7% or 13% from the prior close before 3:25 p.m. ET halts trading for 15 minutes, with no halt at or after 3:25 p.m. A 20% decline at any time halts trading for the rest of the day. On Friday’s close, those levels sit near 7,123, 6,664 and 6,128, so a 1987-size drop would breach the third. Losses can still pile up until each level is hit.
AI Warnings Damper Investor Sentiment
Michael Burry, whose bearish calls we have examined before, wrote in a Substack post, “I continue to believe it is possible the markets are near a major top.” He pointed to leverage built by volatility-targeting and momentum strategies in a low-volatility market and compared it with the lead-up to Oct. 19, 1987. He is bearish on AI-linked stocks and reportedly holds short positions including NVIDIA (NASDAQ:NVDA | NVDA Price Prediction) and Micron Technology (NASDAQ:MU), though he has warned short selling is high-risk.
According to Bloomberg on Oct. 9, Joachim Klement of Panmure Liberum says the AI bubble will burst in 2027 or 2028, with his target implying 36% downside for the S&P 500 by the end of 2027. He is the most bearish of eight strategists Bloomberg tracks; the other seven average about 14% upside. He does not recommend selling now.
The IMF’s Global Financial Stability Report on Oct. 13 warned a sharp correction in AI stocks could spread through global markets, citing elevated AI valuations, higher government borrowing costs and a major cyberattack as possible catalysts. “Resilience is not safety,” said the IMF’s Athanasios Vamvakidis. Temasek CIO Rohit Sipahimalani calls a reversal of the AI trade a key risk.
Fund manager Adrian Day says some conditions mirror 1987, including higher rates, dollar and deficit concerns and an AI sector many consider overvalued, though yields aren’t yet high enough to pull large sums out of stocks. Jim Paulsen, on the Excess Returns podcast Oct. 15, highlighted complacency and a possible “fairly nasty correction,” particularly in new-era stocks, without a recession or all-out bear market. Riding a mania is one thing; knowing when to leave is the harder half, and we covered both in a free bubble survivor’s handbook.
Citigroup (NYSE:C) strategists say solid 2027 earnings can support further gains, and Jefferies (NYSE:JEF) projects the S&P 500 could reach 9,000 by the end of 2027, per Invezz. The market has historically survived its worst days.
Watch third-quarter earnings and AI capital spending for signs the AI trade is strengthening or weakening.
Contact [email protected] for any questions or corrections.
AJ spent 10 years writing about financial markets at The Motley Fool. His coverage centers on technology stocks and the broader macroeconomic trends, from interest rates to geopolitics, that shape where markets are headed next. AJ is drawn to the stories where big-picture economics and individual companies collide.
