What is KDJ? If you're involved in technical analysis, you've probably heard of it at least once. Developed by George Lane, this indicator actually originated from the futures market, but nowadays it's widely used in stock markets, cryptocurrencies, and more.

The interesting thing about KDJ is that it’s not just a tool for determining overbought or oversold conditions; it also combines the concepts of momentum and moving averages. It studies the relationship between high, low, and closing prices to more accurately capture market momentum. There are three lines: K, D, and J, each reacting at different speeds. The J line is the most sensitive, followed by K, with D being the most stable.

Simply put, KDJ is an indicator best suited for short- to medium-term trend analysis. The K and D lines range from 0 to 100, while the J line can go above 100 or below 0. Generally, if the J value exceeds 100, it’s considered overbought; if it drops below 0, it’s considered oversold.

In practical use, a buy signal occurs when, on a weekly chart, the J value drops below zero and then hooks upward, forming a bullish candle. Conversely, a sell signal is indicated when the J value exceeds 100 and then hooks downward, forming a bearish candle. However, the judgment also depends on whether the price is above or below the 60-week moving average. Strategies should shift between bullish and bearish depending on the trend.

There are a few points to be careful about when using KDJ. First, parameter settings. The default is 9, but this tends to be too sensitive, generating many false signals. Empirically, trying values around 5, 19, or 25 can produce better results depending on the stock and timeframe.

Additionally, when entering a strong uptrend or downtrend, the KDJ indicator tends to become sluggish. It’s during sideways or unstable markets that this indicator truly shines. Also, after the K value enters the overbought zone (above 80) or oversold zone (below 20), it can stay there for a while—what’s called a “static” phase. Acting impulsively during these periods can lead to losses.

Experienced traders often say that the J value’s signals are the most reliable. For example, if the J value exceeds 100 for three consecutive days, it indicates a short-term rally; if it stays below 0 for three days, it signals a short-term bottom. These signals don’t appear frequently, but when they do, they tend to be highly accurate. The key with KDJ is to pay close attention to these detailed signals.

There’s also a simple rule: buy on a golden cross (K crossing above D) and sell on a death cross (K crossing below D). However, relying solely on this can lead to buying at high prices or selling at lows. Combining multiple indicators and confirming the trend before making a move is essential.