Recently, I’ve been chatting with many traders and found that everyone’s understanding of the KD indicator is still a bit foggy, especially the details of the KDJ parameter settings. Actually, once you understand the underlying logic, this indicator becomes much easier to use.

Let’s start with the most basic explanation. The KD indicator consists of three parts: RSV is the foundation, which tells you whether the current price is high or low within a certain period. The calculation is (today’s closing price – the lowest price in the past n days) divided by (the highest price in the past n days – the lowest price in the past n days), then multiplied by 100. The default n is 9, so if today’s closing price is the highest in the past 9 days, RSV is 100; conversely, if it’s the lowest, RSV is 0.

The K value is the fast line, which weights today’s RSV and yesterday’s K value. The formula is (yesterday’s K value multiplied by 2/3) plus (today’s RSV multiplied by 1/3). This retains RSV’s sensitivity while filtering out noise. The D value is the slow line, which smooths the K value once more, calculated as (yesterday’s D value multiplied by 2/3) plus (today’s K value multiplied by 1/3). This results in the most stable D value.

Some platforms also display the J value, which is the KDJ indicator. The J value equals 3 times K minus 2 times D. Its purpose is to amplify the divergence between K and D. When J exceeds 100, it indicates extreme overbought conditions; below 0, it indicates extreme oversold conditions. So, fundamentally, KD and KDJ are the same indicator, just presented differently.

When I use the KD, most of the time, KD alone is enough. Although J reacts faster, it produces too many false signals and can be easily fooled.

Now, let’s discuss the core issue of the KDJ parameter settings. Why does everyone use the 9,3,3 set of parameters? It’s not just randomly chosen. The first 9 represents using the past 9 candles for calculation. In traditional finance, 9 days roughly correspond to two weeks of trading days, enough to capture short-term fluctuations without reacting too slowly. The two 3s represent the smoothing periods for K and D. The first 3 is a 3-day moving average of RSV, filtering out daily spikes; the second 3 smooths the K value further, making D more stable.

Why has 9,3,3 become the mainstream? First, because in stock and forex markets, it provides the best prediction for oscillating markets, and both golden crosses and death crosses can be used to determine entry points. Second, because everyone uses the same parameters, it creates a collective consensus. When traders all look at the same KD indicator, support and resistance signals become more effective.

However, the KDJ parameters are not set in stone. If you’re doing short-term day trading, you can change it to 5,3,3. This will generate more frequent golden and death crosses, but you need to combine it with other technical analysis tools to filter out noise. If you prefer swing trading and don’t want to be stopped out by daily fluctuations, you can extend the period to 18, making the curves of K and D much smoother. Crosses will only appear when the major trend truly reverses.

Different timeframes also require different KDJ parameter settings. For 5-minute and 15-minute charts, I usually use 14,3,3 to filter out noise; hourly and daily charts are best with 9,3,3 for balanced signals; weekly and monthly charts also use 9,3,3, with fewer signals but greater power, suitable for long-term positioning.

Many people ask me if setting parameters more finely makes the indicator more accurate. Actually, not necessarily. I’ve seen people set parameters to 3,2,2, resulting in countless crosses every day, leading to overtrading and heavy losses. Adjusting parameters is about fitting your trading strategy, not predicting the future.

For most investors, the default 9,3,3 is sufficient. Unless you have a clear reason to change it, don’t easily abandon the collective consensus of that set. KD over 80 is considered overbought, below 20 oversold, but different markets may require slight adjustments.

Ultimately, understanding the calculation logic and the meaning of the parameters behind the KD indicator can help you find your own trading rhythm in choppy markets. Especially the classic default 9,3,3 not only fits most markets but also benefits from collective consensus, making support and resistance judgments more precise. Lastly, remember that this is just an explanation of a technical analysis tool and does not constitute investment advice. Trading decisions should be based on your own situation and risk tolerance.