Average Directional Index (ADX): measuring trend strength

The Average Directional Index (ADX) measures how strongly a market is trending, on a scale from 0 to 100, without saying which way. A stock falling hard and a stock rising hard can both show an ADX of 45. A stock drifting sideways shows an ADX in the teens. J. Welles Wilder Jr. introduced it in 1978 as the centrepiece of his Directional Movement System, the same book that gave us the RSI and the Parabolic SAR.

That directionless design is what makes the ADX useful. Most indicators work well either in trends or in ranges, and fail in the other. The ADX tells you which of those two environments you are in, so you can decide which tools to trust. This guide builds the ADX from its parts, explains the common 20, 25 and 40 readings, and walks through Exxon Mobil's 2026 chart, where the ADX peaked seven weeks before the price did.

What ADX measures

Imagine comparing each day's range with the day before. If today's high pokes well above yesterday's high while the low holds, buyers are pushing price to new territory: that is upward directional movement. If today's low breaks below yesterday's low while the high does not rise, that is downward directional movement. Wilder counted only the larger of the two each day.

Averaged over two weeks and compared with the average true range, these give two lines:

• +DI (plus directional indicator): the share of recent range made by upward pushes.
• −DI (minus directional indicator): the share made by downward pushes.

When one DI is far above the other, movement has been one-sided: a trend. When they are close together, the pushes have cancelled out: a range. The ADX turns that gap into a single smoothed number.

The formula

The Directional Movement Index (DX, +DI, −DI): a hand calculation page works through DM, TR, the DIs and DX by hand on a real JPMorgan bar. Here the focus is the last step, how ADX smooths DX.

A worked example on Exxon Mobil

ADX is a slow average of DX: each day it keeps 13/14ths of yesterday's value and adds 1/14th of today's DX. Suppose ADX is 40 and the trend suddenly becomes perfectly one-sided, with DX at 100 every day:

Even with the strongest possible input, ADX climbs about 4 points a day at first, then more slowly. In practice DX is never 100 for long, which is why ADX readings above 60 are rare. Exxon Mobil (XOM) is a real example of a fast climb: its ADX rose from 16.0 on December 31, 2025 to 45.1 on January 30, 2026 and 58.2 on February 11, while the stock ran from $120.34 to $155.56, a 29% gain in six weeks.

Reading ADX levels

There is no physical law behind the thresholds, but these are the conventions most traders use for a 14-period ADX on daily data:

Direction comes from the DIs. ADX 35 with +DI above −DI is a strong uptrend; ADX 35 with −DI above +DI is a strong downtrend.

Slope matters as much as level. A rising ADX means the trend is gaining strength, whichever way it points. A falling ADX means directional movement is fading. That can be a pause, a slower grind in the same direction, or the start of a range. It does not mean a reversal by itself.

ADX on a real chart: Exxon Mobil in 2026

Exxon Mobil rose about 60% over the year, from $114.69 to $183.29, in two distinct legs with a long, trendless pause between them. The ADX tracked each phase:

• The first leg. ADX first went above 25 on January 15, 2026 (close $129.13) and above 40 on January 28 ($137.58). It peaked at 58.2 on February 11 ($155.56). On 25 days of the year it was above 40.
• Strength fading, price still rising. From the February peak the ADX fell steadily, to 34.7 by mid-March, but Exxon kept climbing to a close of $169.66 on March 31, about 9% above the day of the ADX peak. A trader who read the falling ADX as a sell signal would have left early.
• The pause. In April the stock fell back and −DI crossed above +DI on April 8. By June 11 the ADX had sunk to 10.0, its low for the year, with the stock at $146.60. Between April 30 and June 11 the DI lines crossed eight times. With ADX that low, those crossings were noise, exactly what the ADX was warning about.
• The second leg. From July the ADX rose again, and by late October it was near 30 as Exxon set new highs above $184.

How traders use ADX

As a regime filter. The most common use: trade trend-following signals (moving-average crossovers, breakouts, the Parabolic SAR: how stop-and-reverse works, step by step) only when ADX is above 20–25, and trade mean-reversion signals (oversold bounces, range edges) only when it is below 20. Wilder himself proposed the ADX partly to choose which markets suit trend systems.

DI crossovers with an ADX condition. Wilder's own entry rule bought when +DI crossed above −DI and sold short on the opposite cross, using the extreme of the crossing day as a stop. Practitioners usually add a condition that ADX is above 20 or rising, which removes most of the whipsaws seen on Exxon in May and June.

Peaks in ADX. A very high ADX that turns down often marks the point where a trend shifts from acceleration to consolidation. As the Exxon example shows, that is a statement about momentum, not a forecast of a reversal.

Pitfalls and limitations

Lag. ADX is a smoothed average of a value that is itself built from smoothed averages. It confirms a trend that is already under way; it rarely flags one at the start.

Direction-blindness misleads beginners. A high ADX in a falling market is a strong downtrend, not a bullish sign. Always read it with the DIs or with price.

Gaps and spikes. One huge range day can push the TR and one DM up sharply, lifting DX and then ADX for days afterwards.

ADX compared with related indicators

The Directional Movement Index (DX, +DI, −DI): a hand calculation and the ADXR (Average Directional Movement Rating): what it adds pages cover DX and ADXR in detail.

How Finabase calculates and scores the ADX

Finabase computes ADX with TA-Lib's ADX function on each bar's high, low and close, using Wilder's smoothing. A new ADX study defaults to 14 periods and is drawn in its own panel below the price chart. Finabase does not plot +DI and −DI as separate studies, so direction is read from price, a moving average or the Aroon indicators.

ADX (14) appears in the technical gauge on the symbol page with its latest value, but it carries no Buy or Sell rule: it always counts as neutral. That is deliberate, and faithful to what the ADX measures. A strong trend can point either way, so a high ADX cannot be scored as bullish or bearish on its own.

Frequently asked questions

What is a good ADX value?

Above 25 is the common threshold for a trending market and above 40 for a strong trend. Below 20 usually means the market is ranging. These are conventions for a 14-period ADX on daily charts, not fixed rules.

Does a falling ADX mean the price will fall?

No. It means the trend's directional strength is fading. Price can keep rising slowly, as Exxon Mobil's did for seven weeks after its February 2026 ADX peak, or move sideways.

How do I tell trend direction with ADX?

Use +DI and −DI: the one on top shows the dominant direction. Without them, compare price with a moving average; ADX alone is directionless.

Why is ADX so slow?

It is an average of DX, and DX is built from averaged directional movement and true range. Two layers of Wilder smoothing make it steady and late by design.

Summary

The ADX distils Wilder's directional movement into one number for trend strength. It rises in any strong trend, up or down, and sinks in ranges. Exxon Mobil's 2026 chart shows all three things to know: it confirms a trend after it starts, it can peak long before price does, and a low reading is a warning that crossover signals are mostly noise. Read it first, then choose the tool that suits the market it describes.