S&P 500 · September 11, 1986
The September 1986 drop
-4.81%
single-day change vs previous close
What happened that day?
- On 11 September 1986 the S&P 500 fell 4.81% in a single day
- At the time it was one of the worst single-day falls since 1929
- Selling began on worries about rising rates and a weakening dollar
- Program trading — computer-generated orders — then amplified the fall. It was a technique spreading at the time
- This was the first warning that program trading could amplify a market move
- The warning was not taken seriously enough. A year later the same mechanism produced Black Monday on a far larger scale
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.