Average Directional Index (ADX)

The average directional index (ADX) is a technical analysis indicator that measures how strong a price trend is, on a scale from 0 to 100, regardless of whether prices are rising or falling. It is usually plotted with two companion lines, the positive directional indicator (+DI) and the negative directional indicator (−DI), which show whether upward or downward movement is dominating. Together they make up what is often called the directional movement system.

The ADX was developed by the American technical analyst J. Welles Wilder Jr. and published in his 1978 book New Concepts in Technical Trading Systems, which also introduced the relative strength index and the average true range. Traders use the ADX to decide whether a market is trending, and therefore suitable for trend-following strategies, or moving sideways, where range-trading methods may work better. It is often compared with the Aroon indicator, another trend tool.

Think of the ADX as a wind gauge rather than a weathervane. A weathervane tells you which way the wind is blowing; a wind gauge tells you how hard. The ADX measures how forcefully prices are moving in one direction, whichever direction that is.

The two helper lines act as the weathervane. If the "up" line is above the "down" line, buyers are in control; if the reverse, sellers are. A high ADX reading with the up line on top suggests a strong rise; a high reading with the down line on top suggests a strong fall.

The calculation runs in several steps, usually over 14 periods:

1. Directional movement. For each period, +DM is today's high minus yesterday's high, and −DM is yesterday's low minus today's low; only the larger is counted, and negative values are set to zero.
2. True range. The largest of today's high minus low, the gap from yesterday's close to today's high, and the gap from yesterday's close to today's low.
3. Directional indicators. Smoothed +DM and −DM are divided by smoothed true range and multiplied by 100 to give +DI and −DI.
4. Directional index. The DX compares the two lines.
5. Averaging. The ADX is a smoothed moving average of DX.

The directional index is:

For example, if +DI is 30 and −DI is 10, DX is |30 − 10| ÷ (30 + 10) × 100 = 20 ÷ 40 × 100 = 50. If DX values over recent periods stay around 50, the ADX will also be near 50, signalling a strong trend, here dominated by upward movement.

• Below 20. A weak or absent trend; prices may be moving in a range.
• Above 25. A trend is generally considered established, whether a rally in a bull market or a sustained decline.
• Above 40 to 50. A very strong trend, which some traders see as at risk of exhaustion.
• Rising ADX. The trend is strengthening, whichever its direction.
• Falling ADX. The trend is losing force, even if prices are still moving.
• DI crossovers. +DI crossing above −DI is read as a bullish signal, and the reverse as bearish, especially when ADX is above 20 or 25.

Thresholds vary by market and time frame, and many traders adjust them through testing.

The ADX is available on most crypto charting platforms and is widely built into crypto trading bots and algorithmic trading systems as a filter: for example, a bot might follow trend signals only when ADX is above 25 and switch to buying near support and selling near resistance when it is below 20, as in an ascending channel. Crypto markets trend strongly at times and chop violently at others, so the indicator can help separate the two regimes. Because crypto trades around the clock and many tokens have thin markets, short-period ADX readings can be noisy, and sudden liquidation-driven moves can spike the indicator briefly.

The ADX lags, because it is built from smoothed averages; by the time it confirms a trend, much of the move may have happened. It says nothing about direction on its own, so it must be read with the DI lines or price. A high ADX can persist after the trend has peaked, and a low ADX can precede sudden breakouts. Like all technical indicators, it describes past price behaviour and does not predict future prices; traders combine it with volume, volatility measures and risk controls such as a stop-loss order.