Stochastic oscillator explained: %K, %D and the 20/80 cross, tested
8 min read · Updated 2026-09-29
The stochastic oscillator shows where the latest close sits within the range of the last 14 candles, on a scale of 0 to 100. A close at the top of the range gives 100, at the bottom 0. The idea, from George Lane in the 1950s, is that closes tend to sit near the top of the range in an uptrend and near the bottom in a downtrend.
The usual signal is a crossover of its two lines, %K and %D, inside the extreme zones: below 20 (buy) or above 80 (sell). We measured it on real charts. Across our 41 markets, the four textbook indicators in this series - the stochastic among them - worked 49-51% of the time on the hourly chart. The chart, scoreboards and streak comparison are below.
See it on a real chart: Gold (XAUUSD) liquidation heatmap — the modeled clusters above and below the current price.
How %K and %D are calculated (slow stochastic 14/3/3)
- Raw %K = (close − lowest low of the last 14 candles) / (highest high − lowest low) × 100.
- %K (slow) = the 3-candle average of raw %K. This is the line most charts show as %K.
- %D = the 3-candle average of %K - a smoother, slower copy of it.
The fast stochastic plots raw %K directly and is much noisier; most charting platforms default to the slow version with 14/3/3, which is what we use.
How traders use the stochastic
- Crossover in the zones: %K crossing above %D while both are below 20 is read as a buy signal; crossing below while both are above 80 as a sell. This is what we tested.
- Zone exits: some wait for the lines to leave the zone rather than cross inside it.
- Divergence: as with RSI, price and the oscillator disagreeing at extremes. Subjective, and not part of our test.
Like RSI, the stochastic can stay pinned near 100 or 0 in a strong trend. A reading above 80 describes where the close sits in the recent range; it does not say the range has to break down.
What we measured: stochastic crosses on real charts
A buy signal is %K crossing above %D with both below 20; a sell is %K crossing below %D with both above 80. For each one, a signal counts as a win if price moved one average true range (ATR) in its direction before it moved one ATR against it, within 48 candles, and as a loss if the reverse happened first.
How the signals did in the last month
Now: 3 wins in a row · longest 3 wins, 7 losses
Could be luck — chance alone gives 35–65% over 44 signals
A run does not make the next signal likelier to win — we checked 15,192 signals.
Now: 1 win in a row · longest 4 wins, 4 losses
Could be luck — chance alone gives 35–65% over 44 signals
A run does not make the next signal likelier to win — we checked 15,192 signals.
Now: 1 win in a row · longest 3 wins, 8 losses
Worse than luck — chance alone gives 34–66% over 36 signals
A run does not make the next signal likelier to win — we checked 15,192 signals.
Now: 1 win in a row · longest 4 wins, 5 losses
Could be luck — chance alone gives 37–63% over 53 signals
A run does not make the next signal likelier to win — we checked 15,192 signals.
The roulette view: the indicator next to a coin
Below is every decided signal from the four boards above, one after another, and under it the same number of tosses of a fair coin (a fixed simulated sequence, not re-rolled). Look for the runs: both have streaks of several wins and several losses. A streak is what randomness looks like; it is not a sign that the indicator is “hot” or that a win is “due”.
Streaks: why the stochastic can look perfect for a week
In a range-bound market, buying the low crosses and selling the high ones can produce a satisfying run of wins - until the range breaks and the same rule produces a run of losses. The real sequence above and the simulated coin under it both show such runs. In 100 tosses of a fair coin, a run of six or seven of the same side is normal.
A losing run does not make the next signal likelier to win: across 15,192 hourly signals on 41 markets, after one to five losses in a row the next signal worked 41-56% of the time, within what chance produces.
What that means in practice
- The stochastic is a precise description of where price closed within its recent range. On our data, the 20/80 crossover on its own is not a forecast.
- Combining it with RSI or MACD adds little independent information: all three are calculated from the same recent candles.
- Judge any rule by many signals against a fair baseline.
Each market page shows the stochastic's scoreboard for that market on four timeframes - for example the S&P 500 signal truth section. Moving averages, MACD and RSI are covered in the other articles of this series.
Educational content, not financial or investment advice. Nothing here is a recommendation to buy or sell anything. Figures describe history and models, not what will happen. Trading leveraged products such as CFDs, forex and crypto derivatives carries a high risk of losing money.
See it on a chart
The Gold liquidation heatmap is free on a 24-hour delay — and live for 7 days when you create a free account. No card.