How much should I cut my position size when ADX shows the market isn't trending?

How this is calculated

• ADX (Average Directional Index) measures trend strength on a 0 to 100 scale, regardless of direction. It does not tell you whether the trend is up or down, only how strong it is.
• The commonly cited Wilder guideline treats readings below 20 as a weak or absent trend, 20 to 25 as a developing trend, 25 to 40 as a strong trend, and above 40 as a very strong, and often extended, trend.
• The size adjustment factor applied here is a simplified, commonly used discretionary guideline, not a mathematical formula: 0.5x in a weak trend, 0.75x in a developing trend, 1.0x (your full planned size) in a strong trend, and 0.75x again once the trend looks very strong, since extended trends are more prone to a sharp reversal.
• Many trend-following and breakout traders reduce size or skip new breakout entries entirely when ADX is low, since choppy, directionless conditions tend to produce more false signals.