Recently reviewing some classic technical indicators, I found that the KDJ indicator is indeed worth studying in depth. Many traders have heard of the "Three Treasures of Retail Investors," and the KDJ indicator is one of them. Why is it so popular? Mainly because this indicator is simple and practical, capable of effectively grasping market trends.

First, let's talk about what the KDJ indicator actually is. It is also called the stochastic indicator, composed of three lines: K line (fast line), D line (slow line), and J line (direction-sensitive line). The K and D lines are used to judge overbought and oversold conditions, while the J line reflects the deviation between the K and D lines. Theoretically, when the K line breaks above the D line, it indicates an upward trend and a potential buy signal; conversely, a break below suggests a sell signal.

The calculation logic of the KDJ indicator is actually simple. First, calculate the raw stochastic value (RSV), with the formula RSVn = (Cn - Ln) ÷ (Hn - Ln) × 100, where Cn is the closing price, Ln is the lowest price, and Hn is the highest price. Then, use a smoothing moving average method to calculate the K, D, and J values. In practice, the parameters are usually set to (9,3,3); higher values make the indicator less sensitive to price fluctuations.

How to use the KDJ indicator to identify trading opportunities? I’ve summarized a few practical methods. First is overbought and oversold judgment: when the K and D lines rise above 80, the stock is in an overbought state; falling below 20 indicates oversold. You can also look at the J line: a J value greater than 100 indicates overbought, less than 10 indicates oversold.

More importantly, look for golden crosses and death crosses. A golden cross occurs when the K and D lines are both below 20, and the K line breaks upward through the D line, signaling a buy. A death cross occurs when both lines are above 80, and the K line breaks downward through the D line, signaling a sell. Additionally, pay attention to divergence phenomena. Top divergence occurs when the price hits a new high but the KDJ indicator hits a new low, usually indicating a reversal; bottom divergence is the opposite, with the price hitting a new low but the KDJ indicator hitting a new high, indicating a rebound.

The KDJ indicator also shows top and bottom formations. Double bottoms (W-shaped) appearing below 50 suggest an upcoming reversal upward; double tops (M-shaped) above 80 suggest an upcoming reversal downward. More bottoms indicate a larger upward potential, more tops suggest a larger downward move.

The 2016 Hang Seng Index trend is a good example. At that time, the Hang Seng Index was falling all through February, which looked hopeless to most people, but smart traders noticed that while the price kept making lower lows, the KDJ indicator was making higher lows—classic bottom divergence. On February 19, the Hang Seng opened with a large bullish candle of 965 points, a 5.27% increase, demonstrating the power of bottom divergence. Then, on February 26, a golden cross appeared at a low point, providing an excellent entry point. On April 29, a death cross at a high point prompted timely exit to lock in profits. On December 30, a double bottom pattern appeared, and investors bought the dip again, marking the start of a bull market. This series of operations fully demonstrates the value of the KDJ indicator in practical trading.

Of course, the KDJ indicator is not perfect. It can give early signals that may be false or lagging, especially in extreme market conditions where signals become dull; it also may produce false positives, particularly in sideways or choppy markets, showing unstable performance. Therefore, using the KDJ indicator alone is not enough; it must be combined with other technical indicators and chart analysis for more reliable results.

In summary, the KDJ indicator is an important tool in technical analysis, but no indicator is perfect. Traders need to leverage its strengths in practice and use experience to mitigate its shortcomings. Most importantly, combine the KDJ indicator with candlestick charts and other indicators to better control risk and seize trading opportunities. If you’re interested in deepening your study, practice more on demo accounts to familiarize yourself with how these indicators perform in real market conditions.