While after-hours trading presents investing opportunities, there are also the following risks for those who want to participate:
Inability to See or Act Upon Quotes. Some firms only allow investors to view quotes from the one trading system the firm uses for after-hours trading. Check with your broker to see whether your firm’s system will permit you to access other quotes on other ECNs. But remember that just because you can get quotes on another ECN does not necessary mean you will be able to trade based on those quotes. You need to ask your firm if it will route your order for execution to the other ECN. If you are limited to the quotes within one system, you may not be able to complete a trade, even with a willing investor, at a different trading system.
Lack of Liquidity. Liquidity refers to your ability to convert stock into cash. That ability depends on the existence of buyers and sellers and how easy it is to complete a trade. During regular trading hours, buyers and sellers of most stocks can trade readily with one another. During after-hours, there may be less trading volume for some stocks, making it more difficult to execute some of your trades. Some stocks may not trade at all during extended hours.
Larger Quote Spreads. Less trading activity could also mean wider spreads between the bid and ask prices. As a result, you may find it more difficult to get your order executed or to get as favorable a price as you could have during regular market hours.
Price Volatility. For stocks with limited trading activity, you may find greater price fluctuations than you would have seen during regular trading hours. News stories announced after-hours may have greater impacts on stock prices. As a result, your order may only be partially executed, or not at all, or you may receive an inferior price in extended hours trading to what you might receive during regular market hours.
Uncertain Prices. The prices of some stocks traded during the after-hours session may not reflect the prices of those stocks during regular hours, either at the end of the regular trading session or upon the opening of regular trading the next business day. As a result, you may receive an inferior price in extended hours trading to what you might receive during regular market hours.
Bias Toward Limit Orders. Many electronic trading systems currently accept only limit orders, where you must enter a price at which you would like your order executed. A limit order ensures you will not pay more than the price you entered or sell for less. If the market moves away from your price, your order will not be executed. Check with your broker to see whether orders not executed during the after-hours trading session will be cancelled or whether they will be automatically entered when regular trading hours begin. Similarly, find out if an order you placed during regular hours will carry over to after-hours trading.
Competition with Professional Traders. Many of the after-hours traders are professionals with large institutions, such as mutual funds, who may have access to more information than individual investors.
Computer Delays. As with online trading, you may encounter during after-hours delays or failures in getting your order executed, including orders to cancel or change your trades. For some after-hours trades, your order will be routed from your brokerage firm to an electronic trading system. If a computer problem exists at your firm, this may prevent or delay your order from reaching the system. If you encounter significant delays, you should call your broker to determine the extent of the problem and what you can to get your order executed.