Recently, many people have asked me how to set the KD parameters. In fact, this question reflects that many traders do not have a deep enough understanding of technical indicators. Today, I will clarify the logic behind the KD parameters from the ground up.

Let's start with the basics. The KD indicator consists of three parts: RSV is the foundation, reflecting the current price's relative position within a certain period. Simply put, RSV calculates the position of today's closing price relative to recent high and low points. The formula is (today's closing price minus the lowest price) divided by (highest price minus lowest price), then multiplied by 100. If n=9 by default, and today is the highest point within the past 9 K-bars, RSV is 100; conversely, if it's the lowest point, RSV is 0.

But RSV is too sensitive and produces a lot of noise. That's why we have the K value, which is calculated by taking yesterday's K value multiplied by 2/3 plus today's RSV multiplied by 1/3. This way, it retains sensitivity while filtering out some sudden fluctuations. The K value reacts quickly, so it's called the fast line. Next, the D value smooths the K value again, calculated by taking yesterday's D value multiplied by 2/3 plus today's K value multiplied by 1/3. This makes the D value the most stable slow line.

Some platforms also display a third line called the J value, calculated as 3K minus 2D. The purpose of J 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. Although J reacts quickly, it also produces many false signals. In most cases, the KD indicator alone is sufficient.

Why are the default KD parameters 9, 3, 3? These numbers are not arbitrary. The first 9 represents the period of the past 9 K-bars used for calculation. In traditional finance, 9 days roughly cover two weeks of trading days, capturing short-term fluctuations without being too slow. The two 3s are the smoothing periods for K and D values. The first 3 averages RSV over 3 days to filter out daily spikes; the second 3 smooths the K value again to produce a more stable D value.

The reason 9, 3, 3 became mainstream is because it performs most balanced in volatile markets like stocks and forex, allowing trend judgment and entry signals via golden and death crosses. More importantly, when most traders use the same KD parameters, the support and resistance signals generated are more effective, creating a collective consensus effect.

However, KD parameters are not fixed. If you're doing short-term day trading, you can set them to 5, 3, 3, which will produce more frequent crosses, but you should also combine other technical analysis to filter noise. For more stable swing trading, you can increase the period n to 18, making it 18, 3, 3. This results in smoother K and D curves, with crosses only appearing during major trend reversals.

Different timeframes also have their own rules. For 5-minute and 15-minute charts, using 14, 3, 3 can better filter noise and find short-term rebound signals; hourly and daily charts are best with the default 9, 3, 3 for balance; weekly and monthly charts also use 9, 3, 3, but with fewer signals and greater power, suitable for long-term positioning.

A common misconception I must emphasize is that more finely tuned KD parameters do not necessarily mean higher accuracy. If you set parameters too short, like 3, 2, 2, you'll see countless crosses, leading to overtrading and frequent stop-losses. Adjusting KD parameters should be aligned with your trading strategy, not used to predict the future.

Traditionally, a KD above 80 is considered overbought, below 20 oversold, but these thresholds may need slight adjustments in different markets. Lastly, unless there's a clear reason, do not easily abandon the default parameters. Using non-mainstream settings can cause you to lose the collective consensus effect.

Understanding the logic behind KD parameters can help you find a suitable trading rhythm in choppy markets. Most of the time, the default 9, 3, 3 is already sufficient for most needs.