Recently, many people have asked me about the KD indicator, especially how to understand those parameter settings. To be honest, many traders use the KD indicator without really understanding the underlying logic. Today, I’ll break it down.

The KD indicator actually consists of three layers. The bottom layer is RSV, which is the raw stochastic value. Its function is simple: to see where today’s closing price stands within a certain period. The formula is (today’s closing price minus the lowest price in the past n days) divided by (the highest price in the past n days minus 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 point in the past 9 days, RSV is 100; conversely, if it’s the lowest point, RSV is 0.

Based on RSV, the K value is a smoothed version of RSV, 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 noise. Because K reacts quickly, it’s called the fast line. The D value is then smoothed again from K, using yesterday’s D multiplied by 2/3 plus today’s K multiplied by 1/3, making D more stable. It’s called the slow line.

Some platforms also add a J value, calculated as 3×K minus 2×D. The purpose of J is to amplify the divergence between K and D. When J exceeds 100, it indicates extreme overbought conditions; below 100, it indicates extreme oversold. However, honestly, while J reacts quickly, it also produces many false signals. For most traders, using just KD is sufficient.

Why do most software defaults to 9, 3, 3? It’s not random. The 9 represents using the past 9 candles as the period. In traditional finance, 9 days roughly correspond to two weeks of trading days. This length can capture short-term fluctuations without being too sluggish. The two 3s represent the smoothing periods for K and D. The first 3 is a 3-day moving average of RSV, filtering out noise from daily surges or drops. The second 3 smooths K again. This parameter set became mainstream because it works best in stock and forex markets for predicting oscillations. When everyone uses the same parameters, the support and resistance signals become more effective, demonstrating the power of collective consensus.

Of course, KD settings can be adjusted based on your trading strategy. If you want faster signals for short-term day trading, you can set it to 5, 3, 3. This will produce more frequent golden and death crosses, but also more false signals, so it needs to be filtered with other technical analysis tools. For more stable swing trading, you can extend the period to 18, 3, 3, making K and D curves smoother, with crosses only appearing during major trend reversals.

Different timeframes also have variations. On 5-minute and 15-minute charts, I usually use 14, 3, 3 to filter noise and identify short-term rebounds. On hourly and daily charts, the default 9, 3, 3 offers the best balance, with more reliable crossover signals. Weekly and monthly charts also typically use 9, 3, 3; signals are fewer but more powerful, suitable for long-term positioning.

A common misconception is that the more finely tuned the KD parameters are, the more accurate they become. Actually, not necessarily. Adjusting parameters is meant to match your trading style, not to predict the future. If you set parameters too aggressive, like 3, 2, 2, you’ll see countless crossovers, leading to overtrading and frequent stop-losses. For most investors, sticking to the default 9, 3, 3 is sufficient unless you have a clear reason to change.

Regarding overbought and oversold levels, traditionally, KD above 80 is considered overbought, below 20 oversold. But different markets may require slight adjustments. Lastly, I want to emphasize that there’s no need for everyone to use different KD parameters. Traders use the KD indicator to profit, not to be contrarian. Using non-mainstream parameters may weaken the collective power of consensus signals.

Understanding the calculation logic and the meaning behind the parameters of the KD indicator can help you find suitable trading strategies in choppy markets. Especially the classic 9, 3, 3 setting, which not only fits most market environments but also benefits from collective consensus, making support and resistance signals more precise. So rather than blindly tweaking parameters, it’s better to first grasp the essence of the default settings and then fine-tune based on actual trading results.