Extended-hours trading is stock trading that happens either before or after the normal trading hours of a stock exchange, i.e., pre-market trading or after-hours trading.
Since 1985, the regular trading hours for major exchanges in the United States, such as the New York Stock Exchange and the Nasdaq Stock Market, have been from 9:30 a.m. to 4:00 p.m. Eastern Time (ET). Pre-market trading occurs from 4:00 a.m. to 9:30 a.m. ET, although the majority of the volume and liquidity come to the pre-market at 8:00AM ET. After-hours trading on a day with a normal session occurs from 4:00 p.m. to 8:00 p.m. ET. Market makers and specialists generally do not participate in after hours trading, which can limit liquidity.
Trading outside regular hours is not a new phenomenon but used to be limited to high-net-worth investors and institutional investors like mutual funds. The emergence of private trading systems, known as electronic communication networks (ECNs), has allowed individual investors to participate in after-hours trading.
Financial Industry Regulatory Authority (FINRA) members who voluntarily enter quotations during the after-hours session are required to comply with all applicable limit order protection and display rules (e.g., the Manning Rule and the U.S. Securities and Exchange Commission order handling rules).