S&P 500 Plunged 20.47 Percent

On October 19, 1987, the S&P 500 plunged 20.47% in a single trading day, the only time in modern market history it has lost more than 20% in one session. Fears about overvalued stocks, rising interest rates, and US trade and budget deficits had already shaken investors, while computer-driven portfolio insurance likely accelerated the sell-off. The Federal Reserve supplied emergency liquidity after the crash, and the S&P 500 finally regained its pre-crash high on July 26, 1989.

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