Recently, I saw many beginners in stock market forums getting confused by limit-up and limit-down moves, so I decided to organize my understanding of these phenomena. Basically, limit-up and limit-down are expressions of stock prices moving to their extremes, representing a one-sided buying or selling frenzy in the market.

First, let's talk about how to judge. If you notice on the trading chart that a stock's price movement becomes a straight line, with no change in price, it's basically a limit-up or limit-down. It's easy to distinguish on the Taiwan stock market: limit-up is marked with a red background, and limit-down with a green background. I've seen stocks at limit-up where the buy orders are full, and the sell orders are almost empty, because the demand to buy far exceeds the desire to sell. Conversely, at limit-down, the sell orders are overflowing, and buy orders are sparse.

Many people ask if they can still trade during a limit-up. Actually, yes. When a stock hits the limit-up, placing a buy order doesn't necessarily execute immediately because there are already many people queued at the limit-up price, but placing a sell order is almost instant. The logic is reversed for limit-down: if you place a buy order, it will execute immediately because there are many willing sellers, but if you place a sell order, you'll need to queue. I've experienced situations where a stock is locked at limit-down; the best approach is to place a sell order during the opening auction as quickly as possible because the trading rule is "price priority, time priority," meaning the earlier you place your order, the higher your position. Don't rush to cancel and re-enter orders just because your order hasn't filled; that can push you to the back of the queue. Sometimes, liquidity is released in the last 10 to 15 minutes before market close, with funds coming in to buy cheap shares, which is also the last chance to sell.

In Taiwan, listed and OTC stocks are restricted to a maximum of 10% price change from the previous day's closing price. For example, if a stock closed at 600 NT dollars yesterday, today it can only go up to 660 NT dollars or down to 540 NT dollars.

The reasons for hitting a limit-up are usually several. The most direct is positive news, such as a huge increase in the company's earnings report, receiving large orders, or government subsidies for certain industries, which causes market funds to rush in. Popular themes also play a role, like AI concept stocks or biotech stocks, which are especially easy to hype. Technical strength can also trigger limit-ups, such as a stock breaking out of a long consolidation zone with high volume, or when high short interest triggers a short squeeze, attracting buying interest. Lastly, when the chips are locked in—foreign investors and investment trusts continuously buying large amounts, or major players tightly locking in their positions—the market has few stocks to sell, and a slight push can cause a limit-up.

The reasons for limit-down are more frustrating. Negative news is a major factor, such as poor earnings reports, declining gross margins, company scandals, or industry downturns, which trigger panic selling. Systemic risks also cause limit-downs, like the global COVID-19 pandemic, where many stocks drop to the limit or halt trading. A stock market crash in the US can also drag down Taiwanese tech stocks to limit-down. Additionally, major players may offload holdings—buying high and selling to trap retail investors—margin calls can also cause limit-downs. Technical breakdowns are signals too; breaking below key support levels like the monthly or quarterly moving averages, or sudden high-volume black candles, often indicate major players are unloading, and stop-loss selling pressure can easily lead to limit-down.

By the way, the US stock market does not have a limit-up or limit-down mechanism, but they do have circuit breakers. When the S&P 500 drops more than 7%, the market pauses for 15 minutes; a 13% drop also results in a 15-minute halt; if it falls 20%, trading stops for the day. Individual stocks also have circuit breakers—if their price moves more than 5% within a short period, trading is temporarily suspended.

My advice when encountering limit-up or limit-down situations is to stay calm and assess carefully. Beginners often make the mistake of blindly chasing gains or cutting losses. When facing a limit-down, don't rush to sell; first, clarify whether the company truly has problems or if it's just market sentiment dragging the price down. If the fundamentals are intact and it's only a short-term factor, the price may rebound later. Holding or adding small positions is often the best strategy. When a stock hits limit-up, don’t rush to buy; first confirm whether there is genuine positive news supporting it. If it can't hold, consider waiting.

Another approach is to trade related stocks. When a stock hits limit-up due to positive news, consider buying upstream or downstream suppliers or similar stocks. For example, if a leading semiconductor stock hits limit-up, other semiconductor stocks often move in tandem. Some Taiwanese stocks are also listed in the US; you can place orders through overseas brokers or via proxy, which makes trading more convenient.