%K vs %D, and the smoothing layer

Two lines, one job

Open a stochastic on any chart and you will see two lines in the sub-panel, not one. The faster, twitchier line is %K - the raw oscillator we built in lesson one. The slower, smoother line is %D, and its job is to keep %K honest. %D is a 3-period simple moving average of %K. That is the entire definition. Whenever you read a stochastic, you are watching the relationship between a fast leader and a slow follower.

Why bother smoothing %K at all? Because %K is sensitive. Every new candle close can swing it sharply, especially when the lookback range is tight. A trader reading %K alone is reading a line that reacts to every tick. %D adds three candles of memory, so it only confirms a move once %K has held the direction for a few bars. That tradeoff - faster signal versus cleaner signal - is the entire point of pairing the two.

The default setting on almost every platform is (14, 3). The 14 is the lookback period for %K. The 3 is the smoothing period for %D. You will see this written as 'Stochastic 14, 3' in indicator settings. Some platforms add a third number for an extra smoothing pass on %K itself - that lands you in slow stochastic territory, which we cover in lesson four. For now, hold the simple version: %K is raw, %D is a 3-bar average of %K, and the default lookback is 14.

Crossovers between %K and %D are the canonical trigger. When %K crosses up through %D, that is a bullish signal. When %K crosses down through %D, that is a bearish signal. Lesson three layers the 80 and 20 levels on top so we can talk about overbought and oversold crosses. Lesson four introduces slow stochastic for traders who want even less noise. But the foundation is here: two lines, one job, with the slower line being the one most traders actually act on.

Recap: %K is the raw oscillator. %D is a 3-period SMA of %K. Default setting is (14, 3). %K leads, %D follows. The cross between them is the basic trigger.