Keltner Channels (KC)

Summary

Keltner Channels: three overlap lines around price. The centre line is an exponential moving average of the typical price; the outer bands sit a multiple of the Average True Range above and below it. The band width tracks volatility, so the channel widens in fast markets and narrows in quiet ones.

Formula

TP = (High + Low + Close) / 3 Middle = EMA(TP, N) Band = ATR(M) Upper = Middle + Deviations * Band Lower = Middle - Deviations * Band

Notes

Several incompatible indicators are published under the name "Keltner Channel", disagreeing by percent rather than by rounding. This is the typical-price centre line with a Wilder-smoothed Average True Range band, the form implemented by TTR and ta4j.
Chester Keltner's 1960 original smooths the typical price with a simple moving average and takes the band from the plain daily range; the widely charted modern variant centres on the close instead. Expect a visible difference against a package plotting either.
TTR ties the Average True Range period to the centre line's period. Here the two are independent, so the band width can be tuned separately.
The centre line and the band are separate recursions, each with its own warm-up. They are entered at their own lookbacks, so a caller who wants either one converged sets that function's unstable period — TA_FUNC_UNST_EMA for the centre line, TA_FUNC_UNST_ATR for the band.

Inputs

inHigh — High price of each bar
inLow — Low price of each bar
inClose — Close price of each bar

Outputs

outRealUpperBand — Centre line plus the scaled Average True Range
outRealMiddleBand — Exponential moving average of the typical price
outRealLowerBand — Centre line minus the scaled Average True Range

Parameters

Parameter	Type	Default	Accepted values	Description
`optInTimePeriod`	integer	20	2–100000	Smoothing period of the typical price moving average
`optInATRPeriod`	integer	10	1–100000	Smoothing period of the Average True Range
`optInNbDev`	real	2	any real	Multiplier applied to the Average True Range

Properties

Numerical Stability: Initial Unstable Period — Inherited from ATR and EMA, which KC computes internally; tunable via ATR and EMA's unstable period.


✅ Overlap Input i
☐ Independent Y-Axis
☐ Candlestick
☐ Can Output NaN or ±Inf
☐ Identity at Period 1

Implementation

TA-Lib Definition: kc.c · kc.yaml

Native	File
C	`ta_KC.c`
Rust	`kc.rs`
Java	`Core_KC.java`

TA-Lib is also available for Python, R and more using a wrapper.

Aliases

Keltner Channel