Stochastic Oscillator Calculator (%K and %D)
Calculate Stochastic %K from current close vs N-period high and low range.
Includes overbought 80+ and oversold 20- momentum trading signals.
George Lane developed the Stochastic in the late 1950s. His core insight: in an uptrend, prices close near the high of the range. In a downtrend, they close near the low. The oscillator measures where today’s close sits within the recent high-low range:
%K = 100 × (Close - Low_N) / (High_N - Low_N)
Default N is 14 periods. %K runs from 0 to 100. Above 80 = upper end of range (overbought). Below 20 = lower end (oversold).
%D is %K smoothed. Standard %D is a 3-period simple moving average of %K. Many platforms also smooth %K itself with a 3-period SMA before computing %D — that variant is the “Slow Stochastic.” The version with raw %K is the “Fast Stochastic.” Slow is far more common because raw %K whipsaws too hard.
Lane’s actual signal. People remember Stochastic for the 80/20 levels, but Lane himself said divergences were the real edge. Price making a higher high while %K makes a lower high = bearish divergence, and vice versa. The 80/20 levels are framing, not triggers.
The trap with overbought. Same trap as RSI. In a strong trend, %K stays above 80 for many bars. Selling every print above 80 in a bull run loses money fast. A better rule: only act on overbought/oversold when price has rolled over off the level, not on the first crossing.
Stoch RSI. Some traders apply the Stochastic formula to the RSI value itself, looking at where current RSI sits within its own recent high-low range. It magnifies signals — and noise.
Worked example. Last 14 bars: Highest high = 105.40, Lowest low = 98.20. Current close = 103.10.
- %K = 100 × (103.10 - 98.20) / (105.40 - 98.20)
- %K = 100 × (4.90 / 7.20) = 68.06
That puts close in the upper third of the range but not overbought. Bullish bias, no extreme.