Core terms
Premarket
Extended-hours trading before the 09:30 ET regular open. Exchange premarket sessions start as early as 04:00 ET; the hours a broker allows vary.
US stocks trade in three sessions on a normal day: premarket (from as early as 04:00 ET), the regular session (09:30–16:00) and after hours (usually to 20:00). FINRA warns that extended-hours trading generally has less liquidity, more volatility and wider spreads than the regular session, and that quotes can differ across venues.
Many brokers accept only limit orders in extended hours, and some order types, such as stops, may not trigger. Premarket prices do not set the official open; the opening auction does.
What traders should verify
Check your broker's extended-hours window and which order types it accepts before trading the premarket. Use limit orders and expect larger slippage on market-moving news.
Do not conflate
Broker hours and order rules differ. Overnight or 24-hour sessions offered by some venues and brokers are separate from the exchange premarket session.