Which index did the 1987 Black Monday crash set a record for losing 22.6% in one day?

The Dow Jones Industrial Average set the 22.6% one-day loss record during Black Monday in 1987.

The Dow, commonly called the Dow Jones or simply the Dow, tracks 30 major U.S. companies. On October 19, 1987, it fell 508 points, which represented 22.6% of its previous closing value. The scale of the percentage loss remains notable because the Dow’s point level was far lower than it is in later decades.

Other markets also plunged that day. Hong Kong fell sharply first, European markets followed, and U.S. selling accelerated. The S&P 500 also suffered a major decline, but the famous 22.6% record belongs specifically to the Dow Jones Industrial Average.

The Dow is price-weighted, so companies with higher share prices have more influence than companies with lower prices. That methodology is different from the market-capitalization weighting used by many other broad indexes. Confusing the Dow with the S&P 500 can produce the wrong answer even though both indexes fell during the same crash.