ADX, also from Wilder (1978), measures the strength of a trend without saying anything about its direction. It is built from two directional indicators: +DI (the positive directional indicator) and −DI (the negative one). ADX itself is a smoothed average of |+DI − −DI| / (+DI + −DI).
Typical reads: ADX below 20 = ranging market, ADX above 25 = trending, ADX above 40 = strong trend. The companion +DI / −DI lines are used to read direction — +DI above −DI means the trend is up.
ADX is widely used as a regime filter: only run a trend-following entry rule when ADX is above some threshold. It is slow by design — the default 14-period smoothing means it confirms trends rather than predicting them.
Formula
DX = 100 · |+DI − −DI| / (+DI + −DI) ADX = Wilder-smoothed(DX, N)
Example
+DI = 28, −DI = 12. DX = 100 · 16 / 40 = 40. After Wilder smoothing across 14 bars, ADX settles around 35 — a strong trend.
How Noon Barbari uses Average directional index (ADX)
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See the indicators reference →Related terms
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