Market hours refer to the scheduled times when stock exchanges are open for regular trading. In the United States, the major stock exchanges—the New York Stock Exchange (NYSE) and NASDAQ—operate from 9:30 AM to 4:00 PM Eastern Time on business weekdays (Monday through Friday). These are closed on federal holidays, including New Year's Day, Martin Luther King Jr. Day, Presidents Day, Good Friday, Memorial Day, Juneteenth, Independence Day, Labor Day, Thanksgiving, and Christmas. Occasionally, exchanges close early (at 1:00 PM ET) before certain holidays.

Beyond regular market hours, there are extended trading sessions. Pre-market trading typically runs from 4:00 AM to 9:30 AM ET, and after-hours trading operates from 4:00 PM to 8:00 PM ET. However, extended-hours trading differs significantly from regular hours: trading volume is much lower (meaning fewer buyers and sellers), which can lead to wider bid-ask spreads, greater price volatility, and potentially unfavorable execution prices. Not all securities can be traded during extended hours, and not all brokers offer this capability. Most long-term individual investors conduct transactions during regular market hours when liquidity is highest, and prices are most stable. Extended-hours trading is primarily used by active traders responding to earnings announcements or major news events that occur outside regular market hours.