Pre-market and after-hours explained
Why the US market technically runs sixteen hours, even though only six-and-a-half are 'regular'.
Most US-listed stocks can be traded long before the 09:30 ET opening bell and long after the 16:00 close. These extended-hours sessions exist because institutional traders need to react to news that breaks outside the regular session - earnings reports, geopolitical events, overnight data - without waiting for the next open.
Pre-market: 04:00 - 09:30 ET
Trading is thin until about 07:00, then volume builds as institutional flow comes in. By 09:00, most actively-traded names show meaningful liquidity. The 09:30 opening auction consolidates all overnight interest into a single print.
After-hours: 16:00 - 20:00 ET
The most active hour is 16:00-17:00 ET, when company earnings are reported. Many large-cap names move more in this hour than in the entire regular session that preceded it.
Trade carefully
Limit orders only. Spreads can be five to ten times wider than during regular hours, and a single block trade can move a stock five percent. Retail order types are restricted on most platforms.