The worst day for the markets, in terms of the largest single-day point loss by the Dow Jones Industrial Average, was September 29th, 2008.
It happened when the Dow lost 777.68 points in response to the House’s rejection of the proposed bank bailout plan.
On October 19th, 1987, however, the Dow dropped 22.61% (508 points) in response to a global domino effect of crashing markets. This is the largest single-day percentage drop to date.
Should I Buy the Same Companies Warren Buffett is Buying?
What was the "Flash Crash"?