I just realized that many new investors in stocks do not understand the ceiling price and floor price. Today, I want to share some experiences about how these two concepts operate in the Vietnamese market.

The ceiling price and floor price are pre-calculated levels to control volatility. They are not the actual highest or lowest prices during the session, but boundaries set by the SSC (State Securities Commission). On the electronic price board, you'll see the ceiling price displayed in purple and the floor price in light blue.

The calculation is quite simple. The ceiling price equals the reference price (the previous day's closing price) multiplied by (1 + fluctuation margin). The floor price is the opposite, multiplied by (1 - fluctuation margin). This margin depends on the exchange: HOSE is 7%, HNX is 10%, UPCOM is 15%.

Here's a specific example to make it easier to visualize. If HPG stock has a reference price of 24,000 VND and is traded on HOSE (with a 7% margin), then the ceiling price will be 25,680 VND and the floor price will be 22,320 VND. This example shows that the floor price protects investors from excessive sell-offs within a session.

The advantage of the ceiling and floor prices is that they help prevent price manipulation and wild fluctuations. But there are also issues. When the price hits the ceiling with a large buy order waiting and no sellers, or hits the floor with a large sell order waiting and no buyers, liquidity nearly stalls. At that point, traders can get stuck or miss opportunities.

I often use these signals to make decisions. If a stock hits the ceiling with high buying volume by the end of the session, it indicates strong demand. I might wait for the next session to take profits more effectively. Conversely, if the price hits the floor with low liquidity and bad news, it’s wise to consider selling to avoid risks.

An important note is that the Vietnamese market operates on T+1.5, so you cannot buy and sell immediately within the same session. Analyze the trend carefully when the price hits the ceiling or floor instead of just FOMO following the crowd.

The Vietnamese derivatives market also has ceiling and floor prices, but most international derivatives markets do not. Cryptocurrencies also lack these limits; prices can fluctuate freely according to supply and demand.

Understanding this mechanism will help you trade smarter and avoid common mistakes.