S&P 500 · October 19, 1987
Black Monday
-20.47%
single-day change vs previous close
Part of a longer stretch
The Black Monday slide
midway through · 1987-08-25 → 1987-12-04, -33.51% over the whole period
What happened that day?
- Monday, 19 October 1987 — S&P 500 fell 20.47% in one day (still the record, nearly 40 years on)
- Odd part: nothing major had happened. No war, no big bankruptcy
- Cause was automated selling software, fashionable at the time. It sold once prices dropped past a set level — built to limit losses
- Problem was that everyone ran the same rule. Prices fell so it sold, selling pushed prices lower, so it sold again
- Order volume overwhelmed the exchange. On-screen prices lagged far behind real trades, so nobody knew what anything was worth
- Fell 33.51% from peak to bottom, recovered within two years
- Led US exchanges to adopt circuit breakers that halt trading during steep falls
Sources
Every figure on this page is recomputed from the original daily closing prices and checked against them at build time. The account of what happened is written from the sources listed above.