The Average Directional Index was developed by Welles Wilder and published in 1978. Unlike most indicators that tell you where price might go, ADX tells you how strongly it is trending — regardless of direction. It is the definitive trend strength measurement and the essential filter that separates high-quality trend signals from noise.
Wilder developed ADX as part of a broader Directional Movement System. The system has three components that work together: ADX (trend strength), +DI (positive directional indicator — bullish pressure), and -DI (negative directional indicator — bearish pressure). ADX alone without the DI lines is incomplete.
+DM (Positive Directional Movement) = Current High – Previous High (when positive and greater than -DM, otherwise 0). -DM (Negative Directional Movement) = Previous Low – Current Low (when positive and greater than +DM, otherwise 0). True Range = the largest of: (High – Low), |High – Previous Close|, |Low – Previous Close|.
+DI = 100 × (Smoothed +DM / Smoothed True Range). -DI = 100 × (Smoothed -DM / Smoothed True Range). ADX = 100 × Smoothed moving average of |+DI – -DI| / (+DI + -DI).
ADX measures the absolute difference between +DI and -DI, smoothed over time. When +DI and -DI are far apart — meaning one side is clearly dominating — ADX is high. When they are close together — meaning buyers and sellers are evenly matched — ADX is low. This is why ADX measures trend strength without directional bias.
| ADX Level | Market Condition | Strategy Implication |
|---|---|---|
| Below 20 | Ranging / No trend | Avoid trend strategies — use oscillators |
| 20–25 | Weak trend developing | Trend strategies possible with confirmation |
| 25–40 | Confirmed trend | Strong environment for trend following |
| 40–60 | Very strong trend | High-conviction trend — ride with wide stops |
| Above 60 | Extremely strong trend | Rare — often precedes exhaustion |
The crossover of +DI and -DI is the primary directional signal in the ADX system. When +DI crosses above -DI, buyers are taking control — potential bullish signal. When -DI crosses above +DI, sellers are taking control — potential bearish signal. However, Wilder's critical insight is that crossover signals are only reliable when ADX is above 25 and rising.
Wilder added a specific rule to reduce false signals: When a DI crossover occurs, mark the Extreme Point (the high of the day for a bullish crossover, the low for a bearish). Enter only when price moves beyond that extreme point. Use the extreme point as your stop loss level. This filter eliminates most whipsaw entries from DI crossovers in ranging markets.
The DI crossover without the Extreme Point Rule generates too many false signals. Wilder's own refinement to wait for price to exceed the crossover bar's extreme before entering is one of the most underused risk management tools in technical analysis. Always apply it.
ADX's greatest value is not as a standalone trading signal but as a regime filter that tells you which type of strategy to apply. This single application can transform the performance of any technical trading system.
The slope of ADX matters as much as its level. A rising ADX (even from 15 to 20) indicates trend strength is building. A falling ADX (even from 40 to 35) indicates trend strength is fading. The combination of level and slope gives the most complete picture: ADX at 30 and rising is very different from ADX at 30 and falling.
The classic combination: Use moving averages (20/50 EMA) for trade direction and entry signals. Use ADX as the filter — only take moving average signals when ADX is above 25. This eliminates the majority of false moving average crossovers that occur in ranging markets. In backtests, adding an ADX filter above 25 consistently improves the performance of moving average crossover systems.
ADX above 25 tells you the trend is genuine. RSI's level within that trend tells you the quality of the current entry. In an uptrend (ADX above 25, +DI above -DI), wait for RSI to pull back to 40–50. When RSI turns up from that level, enter long. This combination captures pullback entries in confirmed trends — one of the highest probability setups available.
Wilder's own recommended combination: Use ADX to confirm trend strength (above 25) and use Parabolic SAR for entry and trailing stop within that trend. When ADX drops below 20, stop taking new SAR signals and wait for the trend to re-establish. This was Wilder's personal trading methodology.