Ask TheStreet is designed to answer questions about the market, strategies, and investment methods. Please email us to ask a question, but keep in mind that we cannot offer specific investment advice.


Reader: Every night I watch Cramer's "Mad Money" and watch the stocks he talks about soar in after-hours trading. Who is making those trades, amateurs or professionals? How do these people have access to this type of trading? --T.D.

Gregg Greenberg: Wall Street knows 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. EST and finishes at 4 p.m. But as the earnings avalanche of the last few weeks has shown, it's not as if 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 until the next day to pull the trigger on a trade, there's pre-open and postclose trading on the Nasdaq, as well as a brief late-day "crossing session" on the NYSE.

Institutional investors have long been able to trade after the market, but it's only been about five years since individuals got the privilege. The Big Board and the Nasdaq took up their cause in the late 1990s as electronic networks known as ECNs were expanding their hours and coverage, threatening to take some of the established exchanges' coveted customers.

So when Google ( GOOG) or Yahoo! ( YHOO) puts up its earnings on a Wednesday afternoon or if Jim Cramer's recommendation moves a stock, extended-hours trading gives you a chance to get in on the action before the market has had hours to digest the latest developments.

That said, most professionals caution that individual investors shouldn't wade into these waters without taking stock of the many risks. Stocks that trade heavily after hours tend to be more volatile and to be strongly influenced by breaking news, and volume can be scarce even in some of the bigger names. These factors can lead to wider bid/ask spreads that can drive up the cost of trading in pre-open or postclose markets.

"The danger of trading in extended hours is the thin volume," says Randy Diamond, sales trader at Miller Tabak. "If you are not careful, you could wind up paying well above the market, or selling way below it."

But should you find the need to wade into the world of extended-hours trading, here are the basics.

When Can I Trade?

Nasdaq holds premarket trading from 8 a.m. to 9:30 a.m. and after-hours action from 4 p.m. to 6:30 p.m.

From 4:15 p.m. to 5 p.m., the NYSE holds its so-called crossing session, which means that orders can only be filled if they can be matched (i.e., crossed). Trading is indeed thin, as this session averaged just 43,533 shares per day in 2004, the NYSE says.

How Does It Work?

Actual trades typically take place via computerized order-matching systems known as electronic communications networks. ECNs electronically display and match buyers and sellers to execute limit, not market, orders.

Professional investors, such as institutional investors, have been using ECNs for more than 15 years. Retail investors are commonly discouraged from trading in extended hours because of the lack of liquidity. Nevertheless, most brokers offer retail investors the ability to trade in extended hours if they sign a form stating that they understand the risks. (More about those below.)

Most brokers also maintain restrictions on after-hours trading. Fidelity Investments, for example, has no minimum order but a maximum order of 5,000 shares.

What Moves?

A look at the Nasdaq most actives for the early and late sessions shows that action is concentrated in a few mega-cap names such as Cisco ( CSCO), Microsoft ( MSFT) and Intel ( INTC) -- along with some smaller players that are in the news at the moment, as with earnings reports, executive changes or maybe even a "Mad Money" mention.

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.

If you liked this article you might like

How 1-800-Flowers Preps for Valentine's Day Crush

How 1-800-Flowers Preps for Valentine's Day Crush

Forget Gold and Platinum! Give Your Sweetie Iridium this Valentine's Day

Forget Gold and Platinum! Give Your Sweetie Iridium this Valentine's Day

News Corp. Beats on Bottom Line Despite Sluggish Ad Sales

News Corp. Beats on Bottom Line Despite Sluggish Ad Sales

Nvidia Q4 Beats Street on Top and Bottom Lines

Nvidia Q4 Beats Street on Top and Bottom Lines

Coca-Cola: We'd Like the World to Buy a Coke Zero -- or a Smartwater!

Coca-Cola: We'd Like the World to Buy a Coke Zero -- or a Smartwater!