Halt (LULD)
A mandatory pause in trading when a stock's price moves too far, too fast. LULD bands are set as a percentage of the prior reference price.
A LULD halt (Limit Up-Limit Down) is a temporary suspension of trading triggered automatically when a stock's price moves outside a defined percentage band from a 5-minute reference price. The bands are narrower for S&P 500 and Russell 1000 stocks (5%) and wider for others (10–20%).
When a stock touches the band and stays there for 15 seconds without trading resuming within the band, a 5-minute trading pause is called. After 5 minutes, trading resumes via an auction — unless the halt extends due to continued extreme conditions.
LULD replaced the old single-stock circuit breakers after the 2010 Flash Crash. It slows momentum panics and squeezes, giving market participants time to reassess. Halts on news or regulatory grounds (SEC investigations, merger announcements) follow a separate process.