What is the stochastic oscillator?

%K, %D, and the two settings

The raw calculation gives the %K line. Because raw %K is jumpy, platforms usually smooth it, and then draw a moving average of it called %D. The default is often written 14, 3, 3: fourteen candles of range, three periods of smoothing on %K, three more for %D.

A fast stochastic uses the raw %K. A slow stochastic uses the smoothed one, which is what most charts show by default and what most published rules assume.

The two lines crossing is the classic signal. It is also the least informative part of the indicator, for the reason set out below.

Why the 80 line is not a sell signal

Above 80 is conventionally called overbought, below 20 oversold. Those are labels, not instructions, and here the label is more misleading than on most indicators.

Consider what a reading above 80 actually says: price has been closing near the top of its recent range. In a strong uptrend, that is exactly what you would expect, and it can continue for weeks. The stochastic will pin near its ceiling for the entire move.

So a stochastic stuck above 80 is evidence of a trend, not evidence of a top. Selling each time it enters the zone means selling into strength repeatedly. The same argument applies to the RSI, and it is the same mistake, which is covered from the other side in the guide on the RSI.

The reading has real value in a range, where price genuinely oscillates between two edges. It is the only market where both extremes carry the meaning the labels promise. In a trend, only one of them does: the reading pins against the far end for weeks and says nothing, while the rare visit to the other end is the one worth looking at.

What it does better than a momentum indicator

Because the stochastic is scaled to the recent range, it flattens out how big the moves were. Two markets, one calm and one violent, can both show a stochastic at 90, and in both cases the statement is the same: closes are landing near the top of the recent range.

That makes it a good tool for one specific job. Detecting when a market that had been closing at one end of its range starts closing at the other. That shift often shows on the stochastic before it is obvious on price, because the indicator is measuring position rather than distance.

Divergence, and the honest version of it

Divergence is when price makes a higher high while the stochastic makes a lower one. What it says is precise and modest: the newest high closed less strongly inside its range than the previous one did.

That is worth knowing. It is not a reversal signal. In a trending market divergence appears repeatedly and price keeps going, because closing slightly less strongly is not the same as turning around.

Divergence read at a level where price has already stopped before is a different proposition from divergence in open space. The level does the work; the indicator describes the condition.

The mistakes that cost the most

Using it in a trend as a reversal tool. This is the expensive one. The indicator pins at the extreme for as long as the trend lasts.

Trading every crossover. On the default settings the lines cross constantly. Most crossings are noise inside the same condition.

Running it alongside the RSI. Both measure something closely related. Two indicators that agree because they read the same thing are one indicator with extra steps.

Tuning the period until it fits. The settings that would have caught the last few turns are fitted to the noise you already have.

Questions people ask

What is the difference between the stochastic and the RSI?

The stochastic measures where the close sits inside the recent high to low range. The RSI compares the size of recent gains to the size of recent losses. Related questions, different arithmetic, and they disagree most in exactly the situations that matter.

What are the best stochastic settings?

14, 3, 3 is the default and the one most traders are watching. Shorter periods react sooner and cross more often; longer ones are calmer and later. No setting removes the trade off.

What does a stochastic above 80 mean?

That price has been closing near the top of its recent range. In a range that often precedes a turn. In a trend it is simply what a trend looks like, and it can persist for a long time.

Fast or slow stochastic?

Slow, for almost everyone. The fast version uses the raw %K and is noisy enough that the crossings are hard to use. Most published rules assume the slow version anyway.

Reading momentum in context

Trading AI reads a photo or a screenshot of any chart and returns the indicator readings visible in the image, alongside the market structure, the key levels and a full trade plan with its risk. The analysis works from the image, so an indicator panel that is not on screen cannot be read.

The other bounded momentum reading, and the one most often paired with this one: What is the RSI?

Momentum measured as a gap between two averages instead: What is the MACD?

Whether you are in the range the indicator was designed for, or in a trend: What is market structure?

This page is educational. It is not financial advice, and nothing here is a recommendation to buy or sell anything.