Recently, I’ve noticed that many people still have misunderstandings about the KDJ indicator. I’ll discuss what KDJ is and how to use it from a practical perspective.

Actually, KDJ is simply a momentum indicator, originating from the futures market and later widely applied in the stock market. It calculates the relationship between the highest price, lowest price, and closing price over a certain period to determine whether a stock is overbought or oversold. In simple terms, it’s a tool used for bottom fishing and topping out. The default period is 9 days, but you can adjust it yourself.

In terms of its form, KDJ consists of three lines: K, D, and J, representing the speed of price changes. Here’s a core concept to understand: K and D values operate between 0 and 100, with 50 as the dividing line—above 50 indicates bullishness, below 50 indicates bearishness. The J value is the most sensitive, capable of breaking above 100 or dropping below 0.

In practical use, the most common technique is to watch for golden crosses and death crosses. When the K line crosses above the D line from below, it’s a golden cross, which can be considered a buy signal; conversely, when it crosses below, it’s a death cross, signaling a sell to avoid risk. But this relies on a prerequisite: it must be combined with moving averages. If the stock price has been under pressure below the moving average for a long time, even a golden cross only indicates a short-term opportunity.

More reliable signals are secondary crossovers. When two golden crosses occur near the 20 level, it indicates the bottom has been confirmed and can be held for medium to long-term. Conversely, two death crosses near the 80 level are clear sell signals. My experience shows that secondary crossovers have a much higher success rate than single crossovers.

There’s also a phenomenon called “refusal of death cross” that’s easy to overlook. During an uptrend, if the KDJ prepares for a death cross but ultimately doesn’t cross, it indicates the selling pressure has been absorbed. This often signals a short-term buying point. If multiple refusal of death crosses occur consecutively, it’s a sign of a potential rally, and the stock usually moves higher.

Regarding the J value, it’s the most sensitive among the three lines. When J stays above 90 for several days, the stock is likely forming a short-term top; when below 10, it indicates a short-term bottom. But be cautious: these signals are best used in conjunction with KD values or other top/bottom patterns, as relying on J alone can be misleading.

An important concept is “dulling,” which refers to the indicator losing effectiveness. In extremely strong or weak markets, KDJ can become overbought or oversold, and it’s best not to rush into buying or selling. Wait for clear golden or death crosses before acting. Many traders prematurely exit during dull periods, missing out on larger subsequent moves.

I also frequently use multi-timeframe analysis. For example, to find good intraday entry points, I look for a golden cross on the 60-minute chart → on the 30-minute chart → and a high-level death cross on the minute chart. This helps avoid selling at the day’s lowest point. The same logic applies for medium- and long-term holdings: stocks with golden crosses on daily, weekly, and monthly charts are the most worth holding.

However, honestly, KDJ isn’t万能 (all-powerful). It’s highly accurate for high-quality stocks, but less suitable for stocks with very low trading volume or newly listed small and medium-sized stocks. These stocks tend to have low liquidity; although KDJ may show large fluctuations, the actual price movements are small, limiting profit potential.

Another point to be cautious about is that major players may use KDJ to shake out traders. They might deliberately suppress the price to generate death cross signals, then quickly push the price up after retail investors sell, turning the death cross into a golden cross. In such cases, it’s best to combine trend lines for judgment. If the price remains above the trend line, it’s likely that the main force is shaking out weak hands, and you shouldn’t panic and sell just because of a death cross.

In summary, the question of “what is KDJ” is really about whether it’s a practical tool. When used properly, it can indeed help you buy at the bottom and sell at the top. But it must be combined with other indicators and market conditions; over-reliance is dangerous. Especially in extreme market conditions, be extra cautious about signals from KDJ—don’t get fooled by overbought/oversold levels or manipulative traps set by big players.