Stochastic Oscillator

Momentum

What it measures

The Stochastic Oscillator compares the current closing price to the high-low range over a lookback period (default 14). It outputs %K (fast) and %D (smoothed signal line) on a 0–100 scale, showing where price closed relative to its recent range. It identifies overbought/oversold conditions and potential reversals.

How readings are interpreted

%K above 80 means price closed near the top of its recent range (overbought). Below 20 means near the bottom (oversold). The key signal is %K crossing %D — above it is bullish, below is bearish. Divergence (price making new highs but Stochastic declining) warns of weakening momentum.

Conventional levels

Above 80: conventionally described as overbought; a bearish %K/%D crossover here is the commonly cited pattern
Below 20: conventionally described as oversold; a bullish %K/%D crossover here is the commonly cited pattern
%K crosses above %D: bullish momentum signal
%K crosses below %D: bearish momentum signal
50 level: midpoint — above = bullish, below = bearish bias

Where it works, and where it does not

Most effective in ranging, non-trending markets. In strong uptrends, overbought readings are continuation signals not reversals. In downtrends, oversold readings keep resetting without bouncing. Use Choppiness Index or ADX to confirm ranging before applying Stochastic.

Commonly read alongside

RSI: Both oversold at the same time = stronger reversal signal
Bollinger Bands: Stochastic oversold + price at lower band = high-conviction bounce setup
Parabolic SAR: Stochastic oversold + SAR flips above price = strong buy trigger

Known limitations

In trending markets Stochastic stays extreme for many bars, so extreme readings are not conventionally read as reversals
Fast Stochastic (%K only, no smoothing) generates too many false signals — %D is the conventional choice
On illiquid assets, large gaps distort the range and make intraday Stochastic unreliable

In practice

Slow Stochastic (%K smoothed with a 3-period SMA) is the usual choice for reducing noise
In swing approaches, oversold readings are conventionally treated as meaningful only while price is above the 200 EMA
The bullish configuration is a higher low in Stochastic against a lower low in price (hidden divergence)
An engulfing candle coinciding with an oversold reading is widely regarded as stronger than either alone

Plot it yourself. Add this indicator to a chart, change every parameter and watch the line move, then backtest how the rule would have behaved on historical data — free on the S&P 500 ETF, no card.

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This is reference material, not advice. It describes what each indicator measures and how its readings are conventionally interpreted. Nothing here is a recommendation to buy or sell anything, and no indicator predicts future prices. GU Analyser is an analytical tool — no money is ever traded here.