In business, the trading day or regular trading hours (RTH) is the time span that a stock exchange is open, as opposed to electronic or extended trading hours (ETH). For example, the New York Stock Exchange is, as of 2020, open from 9:30 AM Eastern Time to 4:00 PM Eastern Time. Trading days are usually Monday through Friday. When a trading day ends, all trading ends and is frozen in time until the next trading day begins. There are several special circumstances which would lead to a shortened trading day, or no trading day at all, such as on holidays or on days when a state funeral of a head of state is scheduled to take place.

The NYSE and NASDAQ average about 252 trading days a year. This is from 365.25 (days on average per year) * 5/7 (proportion work days per week) - 6 (weekday holidays) - 4*5/7 (fixed date holidays) = 252.03 ≈ 252. The holidays where the stock exchange is closed are New Year's Day, Martin Luther King Jr. Day, Presidents' Day, Good Friday, Memorial Day, Juneteenth, Independence Day, Labor Day, Thanksgiving Day, and Christmas Day; there are also some holidays where trading is permitted, including Columbus Day, Veterans Day, and New Year's Eve. For Juneteenth, Independence Day, Christmas Day and New Year's Day if they fall on a weekend day, the next consecutive weekday has the holiday observed and the market closed on that date. Up to three trading days (July 3, the day after Thanksgiving, and Christmas Eve) are shortened, i.e. the exchanges are open from 9:30AM–1:00PM, depending on where they fall in the calendar year (if July 3 or Christmas Eve fall on a weekend, the shortened day is simply skipped).

Juneteenth was added as a national holiday and market holiday on June 17, 2021.