Ask TheStreet: Late Trading

If trading is halted in a given security on the primary stock exchange, then that security will generally not be eligible for trading on the ECN. The rules of Nasdaq and NYSE governing stock halts apply to the extended-hours trading sessions as they do to other sessions.

What Should I Know?

Fidelity warns investors that trading through an ECN in extended hours poses certain risks. These risks include lack of liquidity, greater price volatility and price spreads, limited access to other markets and market information, price variance from standard market hours, the time and price prioritization of orders, and communication delays. These risks may prevent your order from being executed, in whole or in part, or may prevent you from receiving as favorable a price as you might receive during standard market hours.

Price volatility usually refers to the speed and size of changes in the price of a stock. There may be more volatility in the extended-hours sessions than in the standard day session, because of the lack of buyers and sellers.

Price spread generally refers to the difference in prices between what you can buy a security for and what you can sell it for. Lower liquidity and higher volatility sessions may result in wider-than-normal spreads for a particular security.

If that sounds like a bunch of legal nonsense, it boils down to this: Stocks often make big moves in the after hours that don't hold up. So if you're not careful, you can wake up the next morning to find you've lost a bunch of money, mad or otherwise.