Which U.S. market benchmark fell 20.47% on October 19, 1987?

The S&P 500 fell 20.47% on October 19, 1987.

That percentage decline made Black Monday one of the most severe single-day losses in the history of the U.S. stock market. The Dow Jones Industrial Average fell 22.6%, while the broader S&P 500 also experienced an extraordinary collapse.

Several pressures were present, including high valuations, rising interest rates, trade tensions, and concerns about economic conditions. Portfolio insurance and computerized trading may have accelerated selling, although no single explanation fully accounts for the event.

The S&P 500 is often confused with the Dow in accounts of Black Monday. The Dow’s larger percentage fall is more famous, but the S&P 500’s 20.47% loss is a separate, precise benchmark figure. Exchanges subsequently developed coordinated trading halts to slow disorderly declines.