After-hours and pre-market trading
Trading outside the regular exchange session, with thinner liquidity and wider spreads than the main session.
US stock markets have a regular session from 9:30 a.m. to 4:00 p.m. Eastern time. Pre-market trading runs before the open and after-hours trading runs after the close, through electronic networks with fewer participants. Prices set in these sessions are real trades, but they are not the official close.
On our site, extended-hours prices are labeled as such, and the official close is shown separately. Compare extended-hours volume with the regular session before reading a move as meaningful.
Traders care because earnings and major news often land outside the regular session, so extended-hours prices can gap sharply. Thin liquidity means wider spreads, and a single order can move the price more.
Worked example (illustrative numbers, not real data): a stock closes at 100.00 and trades at 106.00 after hours following an earnings release. The 6 percent move looks large, but only 200,000 shares change hands, against 5 million in a normal session, so the price may not hold at the open.