The Average Directional Index (ADX) measures the strength of a trend on a 0-100 scale — regardless of direction. A rising ADX means the trend (up or down) is strengthening; a low, flat ADX means the market is rangebound and directionless. It answers "is there a trend?" before you ask "which way?"

Reading the levels

Broadly: below 20-25 signals a weak or absent trend (choppy, mean-reverting); above 25 signals a trending market that's gaining strength; above 40-50 signals a very strong trend. The ADX line itself has no direction — it only tells you how much conviction is behind the current move.

The DI lines

ADX is usually paired with two directional indicators: +DI (upward pressure) and -DI (downward pressure). When +DI is above -DI, buyers dominate; when -DI leads, sellers do. The combination tells you both the strength (ADX) and the direction (which DI leads) of the move.

ADX doesn't say buy or sell. It says whether it's a day to trend-follow or a day to fade.

Why it's underrated

ADX's real value is regime detection. A momentum strategy works in high-ADX conditions and dies in low-ADX chop; a mean-reversion strategy is the reverse. Knowing which regime you're in — before you apply a strategy built for the other — is one of the quietest edges there is. That's a job systematic reads take seriously.