When I was recently watching the U.S. stock market, I suddenly realized that many people still feel a bit confused about pre-market trading. In fact, U.S. pre-market trading refers to the time period before the New York Stock Exchange and NASDAQ officially open, when investors can enter the market and trade in advance. It typically runs from 4:00 a.m. to 9:30 a.m. Eastern Time. Although this time window may seem insignificant, its impact on the market can be quite substantial.

I noticed that many people don’t know why this pre-market trading session is set up. Put simply, it’s designed to give investors the ability to react to breaking news as early as possible. Imagine that a company suddenly releases a major announcement at night U.S. time, or that the European markets experience sharp volatility—investors can adjust their positions during pre-market hours rather than waiting for the regular trading session and being forced to respond passively. This mechanism is especially important for traders who are seeking an early edge.

Take Alibaba’s incident as an example. On November 16, 2023, Jack Ma and his family trust planned to sell 5 million ADS shares, and the spin-off plans for Hema Fresh and Alibaba Cloud were also halted. As a result, during pre-market trading, Alibaba’s share price fell by more than 8% right away, and the opening price was down 8.67% compared with the previous day’s close. This is the direct effect of U.S. pre-market trading on stock prices—the market had already priced in these negative developments before the official open.

However, there is one key limitation to note: U.S. pre-market trading can only use limit orders, not market orders. Why? Because there are fewer investors participating in this time window, and liquidity is relatively lower—using market orders could easily leave you trapped at unfavorable prices. So if you want to participate in U.S. pre-market trading, you must do so through brokers that support this session—for example, Webull supports the window from 4:00 a.m. until market open, while Charles Schwab is from 7:00 a.m. to 9:25 a.m.

Since we’re on the topic, let me also mention after-hours trading. Essentially, pre-market and after-hours are the extensions at both ends of normal trading hours (9:30 a.m. to 4:00 p.m. ET). After-hours trading runs from 4:00 p.m. to 8:00 p.m., and it also only allows limit orders. Interestingly, after-hours trading often reflects the market’s true price better than pre-market trading. Why? Because after a full day of trading, the market has fully absorbed all kinds of information; price fluctuations during after-hours are usually more stable and closer to the next day’s opening price.

NVIDIA’s performance that day is a good example. During the regular trading session, the stock price swung widely between $461.87 and $472, with more than 2% movement up and down. But when it reached after-hours trading, since no new major information emerged, the price quickly stabilized within a narrow range—this is the price the market ultimately discovered.

If you want to trade during these two periods, my advice is: first, closely follow news events. Pre-market and after-hours are the windows when the market responds to news, so it’s crucial to keep an eye on company announcements and economic data in advance. Second, set a lower buy price or a higher sell price. Because liquidity is thin, sometimes your extreme price can actually get filled, allowing you to profit in the opposite direction. Third, you must control risk. Low liquidity means quotes can be very extreme—so watch out for clearly unreasonable prices and avoid getting trapped.

Of course, although U.S. pre-market trading offers opportunities, it’s not suitable for everyone. If you want more flexible trading hours, you can also consider CFD (contracts for difference). This kind of tool isn’t restricted by exchange hours; it can basically be traded 24 hours a day, and it supports both going long and going short, which is indeed convenient for investors who want to trade around the clock.

Overall, it’s important to understand the mechanism and risks of U.S. pre-market trading. This time window can provide unexpected opportunities, but only if you do your homework, set up stop-losses, and don’t be misled by extreme prices caused by low liquidity. After all, when trading during periods with fewer market participants, the risk and reward are often directly proportional.