An Extended-Hours Trading Primer

Wall Street knows some investors never stop worrying about their holdings. That's why the major exchanges offer extended-hours trading.

The regular trading day, of course, starts at 9:30 a.m. Eastern time and finishes at 4 p.m. But as the earnings avalanche of the last few weeks has shown, it's not like companies stop making news outside those hours. In fact, the vast majority of big news releases are issued either early in the morning or after the close.

So for those who can't stand to wait till the next day to pull the trigger on a trade, there's preopen and postclose trading on the Nasdaq, as well as a brief late-day "crossing session" on the NYSE. ...