ADX Indicator: How to Measure and Trade Trend Strength

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The ADX indicator (average directional index) is a technical indicator that measures how strong a price trend is, on a scale from 0 to 100, without saying which way the trend points. A reading near zero means price is moving without persistent direction. A high reading means one side, buyers or sellers, has been in consistent control over the lookback period. J. Welles Wilder introduced the ADX in his 1978 book New Concepts in Technical Trading Systems, the same work that introduced the RSI and the Average True Range. It works on any market with high, low and close prices, including forex pairs, stocks, ETFs, futures and gold.

What the ADX Measures

The ADX is one part of Wilder’s Directional Movement System. That system has three lines, usually drawn together in one panel below the price chart:

• +DI (plus directional indicator): how much of the recent range came from upward expansion.
• -DI (minus directional indicator): how much came from downward expansion.
• ADX: how far apart +DI and -DI have been, on average, over the lookback period.

The two DI lines show direction. When +DI is above -DI, upward movement has dominated, and the ADX describes the strength of that up move. When -DI is above +DI, downward movement has dominated, and the ADX describes the strength of the down move.

Picture an uptrend that turns into a downtrend. As the rally stalls, the DI lines converge and the ADX falls, even though price may still be near its high. After -DI crosses above +DI and selling becomes persistent, the ADX rises again, this time measuring the decline. The ADX line alone shows “strong, weaker, strong again.” Only the DI lines show that the second strong phase is a downtrend.

How the ADX Is Calculated

The default period is 14, which Wilder used. The calculation has five steps.

Step 1: Directional movement (+DM and -DM). For each bar, compare it to the previous bar:

• Up move = current high minus previous high
• Down move = previous low minus current low

If the up move is larger than the down move and greater than zero, +DM equals the up move. Otherwise +DM is zero. If the down move is larger than the up move and greater than zero, -DM equals the down move. Otherwise -DM is zero. Only one of the two can be positive on any bar. An inside bar, where neither the high nor the low expands, gives zero for both.

Step 2: True range (TR). True range is the largest of:

1. Current high minus current low
2. The absolute value of current high minus previous close
3. The absolute value of current low minus previous close

The second and third measures capture gaps, so a bar that opens well away from the prior close still registers its full movement. TR is also the basis of the Average True Range indicator.

Step 3: Smooth and normalize (+DI and -DI). Smooth +DM, -DM and TR over 14 periods using Wilder’s smoothing, then divide:

• +DI14 = (smoothed +DM14 ÷ smoothed TR14) × 100
• -DI14 = (smoothed -DM14 ÷ smoothed TR14) × 100

Dividing by true range turns raw price distances into percentages. That lets the indicator compare a quiet market with a volatile one, and a currency pair quoted to four decimals with an index quoted in thousands of points.

Wilder’s smoothing for a running total is: new value = previous value minus (previous value ÷ 14) plus current value. It behaves like an exponential moving average with a long effective memory. For a 14-period setting, it is roughly comparable to a 27-period exponential moving average.

Step 4: Directional movement index (DX).

DX = (|+DI − -DI| ÷ (+DI + -DI)) × 100

DX measures how separated the two DI lines are relative to their combined size. When the lines are equal, DX is 0. When one line is near zero and the other is not, DX approaches 100. This is why the ADX can never fall below 0 or rise above 100.

Step 5: Average directional index (ADX). The first ADX value is the simple average of the first 14 DX values. After that:

ADX = ((previous ADX × 13) + current DX) ÷ 14

Because the DI lines need 14 bars and the ADX then averages 14 DX values, the first meaningful ADX appears after roughly twice the period length, about 27 to 28 bars with default settings.

Worked example (hypothetical)

Take two consecutive hourly bars on a currency pair:

• Up move = 1.1080 − 1.1050 = 0.0030
• Down move = 1.0990 − 1.1010 = −0.0020
• The up move is larger and positive, so +DM = 0.0030 and -DM = 0.
• TR = the largest of 0.0070 (high minus low), 0.0060 (high minus previous close) and 0.0010 (low minus previous close), so TR = 0.0070.

Now assume that after adding this bar, the smoothed 14-period totals are +DM = 0.0180, -DM = 0.0090 and TR = 0.0600. Then:

• +DI = 0.0180 ÷ 0.0600 × 100 = 30
• -DI = 0.0090 ÷ 0.0600 × 100 = 15
• DX = |30 − 15| ÷ (30 + 15) × 100 = 33.3

If the previous ADX was 24, the new ADX = (24 × 13 + 33.3) ÷ 14 = 24.7.

The current bar’s DX is 33, a clear separation in favor of buyers, yet the ADX rises less than one point. It takes a sequence of bars with consistently separated DI lines to push the ADX through 25.

Settings: DI length and ADX smoothing

Some charting platforms split the period into two inputs. One is the DI length, the lookback for +DI and -DI in steps 1 to 3. The other is ADX smoothing, the number of DX values averaged in step 5. Both default to 14 in the classic version.

A shorter setting, such as 7 or 10, responds faster to new trends but produces more readings that cross thresholds and then fall back. A longer setting, such as 20 or 30, gives a steadier line that confirms trends later. A level of 25 on a 7-period ADX does not mean the same thing as 25 on a 30-period ADX, so fixed thresholds should be tested against the setting actually in use.

How to Read ADX Values

The standard bands are conventions that traders use, not boundaries built into the formula:

Some traders use 20 as the line between trending and non-trending, others use 25, and many treat 20 to 25 as a gray zone. Using 20 gets a trader into moves earlier, at the cost of more signals that do not develop.

The direction of the line matters as much as its level:

• Rising ADX: the DI lines are separating, so the dominant side is gaining control.
• Falling ADX from a high level: the trend is still in place but losing strength. Price can keep advancing while the ADX declines, because the move is getting less one-sided, not necessarily reversing.
• Low and flat ADX: neither side is in control. A reading of 13, for example, describes a market moving sideways or in overlapping swings, where trend-following entries are poorly suited.

Very high readings deserve care. An ADX above 50 shows an extremely one-sided trend, which may also mean the move is stretched. The ADX often peaks and turns down when a strong trend pauses or corrects, so a turn lower from a very high level can be an early sign that the pace is fading.

Trading with the ADX

Read price first, then use the ADX to judge how persistent the current move is. It serves as a filter and confirmation tool rather than a standalone signal generator.

Choosing between trend and range tactics

• ADX above 25: trend-following methods are more suitable. These include buying pullbacks in an uptrend, selling rallies in a downtrend and moving average crossover systems.
• ADX below 20 for an extended stretch: range conditions. Trend entries tend to get chopped up, while buying near support and selling near resistance fits the market’s behavior better.

A low ADX does not identify where the range boundaries are. That still comes from the price chart.

Confirming DI crossovers

Wilder’s original signals came from the DI lines. A cross of +DI above -DI suggests a long entry, and a cross of -DI above +DI suggests a short entry. The ADX acts as the strength filter:

• Long: +DI crosses above -DI and the ADX is above 25, or above 20 for an earlier entry.
• Short: -DI crosses above +DI and the ADX is above the same threshold.

DI lines cross often when the market lacks direction, and many of those crosses reverse within a few bars. Requiring a minimum ADX screens out crosses in flat conditions. Some traders also require the ADX to be rising at the time of the cross.

Wilder paired these crossovers with an “extreme point” rule. After a crossover, the high (for longs) or low (for shorts) of the crossover bar becomes a reference level. The trade is taken only if price moves through it, and that level can serve as a stop.

Confirming breakouts

Strong trends often start from consolidation, which shows up as a low ADX. When price breaks out of a range and the ADX rises from below 20 to above 25, the breakout has directional persistence behind it. If the ADX stays below 20, or stalls between 20 and 25, the move lacks the follow-through of a sustained trend, and the risk of a failed breakout is higher.

Some traders add volume as a second check, looking for a rising ADX together with rising volume on the breakout. The same approach applies to chart patterns such as a triangle pattern, where the ADX typically falls during the contraction and the breakout is the moment to watch for it turning up.

Momentum peaks and divergence

A sequence of ADX peaks gives a picture of trend momentum over time:

• Higher ADX peaks: each push in the trend is more forceful. This is the condition in which traders are more willing to let a position run.
• Lower ADX peaks: each push is weaker. Any peak above 25 still registers a strong trend, but the declining sequence is a warning.

When price makes a higher high while the ADX makes a lower high, trend strength is not confirming the move. This negative divergence is not a reversal signal on its own. It can be followed by continuation, sideways consolidation, a correction or a reversal. Traders typically respond by managing risk on an open position, for example by tightening a stop or taking partial profits, rather than reversing the trade.

A rising ADX during an established trend can also support adding to a position or trailing a stop in the direction of the move.

Example: the ADX on a gold chart (hypothetical)

A trader watches XAU/USD on a one-hour chart. Gold has been trading between 2,400 and 2,450 for several sessions. The ADX has drifted down to about 15, and the DI lines keep crossing each other. Those readings describe a range, so the trader avoids trend entries.

Then +DI crosses above -DI, and the ADX begins to turn up from its low. That crossover is not yet a trade, because the ADX is below 20. Over the next few bars, gold closes above 2,450, the top of the range, and the ADX moves through 25. The trader now has a breakout on price, +DI above -DI and a confirmed strong reading, so they go long with a stop back inside the range.

Over the following sessions the ADX climbs into the 40s and 50s while +DI stays above -DI. The trader holds the position. Later, gold makes a slightly higher high, but the ADX peak is lower than the previous one and the line turns down. Price begins to move sideways in a narrow band. The trader reads this as fading strength. They tighten the stop, and when the sideways movement continues and the ADX keeps falling, they close the trade.

ADX vs Related Indicators

ADX vs DMI. The Directional Movement Index (DMI) is the full system: +DI, -DI and, in most platforms, the ADX line. The ADX is the strength component. The DI lines are the direction component. On some platforms “DMI” shows all three lines and “ADX” shows only the single strength line.

ADX vs DX. DX is the raw, unsmoothed spread between the DI lines for each bar, and it jumps around. The ADX is DX smoothed over the period.

ADX vs ADXR. Wilder also defined the Average Directional Movement Index Rating (ADXR): the current ADX plus the ADX from a set number of periods earlier, divided by two. It is smoother still and lags more. It is mostly used to compare trend strength across markets.

ADX vs ATR. Both use true range, but they answer different questions. ATR measures how much a market moves, its volatility, in price units. The ADX measures how one-sided that movement is. A market can have a high ATR and a low ADX if it swings wildly back and forth. It can also have a modest ATR and a high ADX if it grinds steadily in one direction.

ADX vs RSI and MACD. The RSI and MACD are directional momentum tools. Their readings rise in rallies and fall in declines, and the RSI is often read for overbought and oversold levels. The ADX has no such zones and rises in both rallies and declines. A common pairing uses the ADX to decide whether the market is trending, then an oscillator for timing: range signals when the ADX is low, pullback entries in the trend’s direction when it is high.

Limitations of the ADX

• It lags. Because it is smoothed twice, it confirms trends after they are underway and signals weakening after the peak in momentum.
• It is non-directional. A high ADX in a sharp sell-off looks the same as a high ADX in a rally, so read it with the DI lines and the price chart.
• It does not predict. A strong reading does not guarantee the trend will continue, and a low reading does not say which way the next breakout will go.
• DI crossovers whipsaw in ranges. The ADX filter reduces these signals but does not remove them.
• Thresholds are not universal. How often a market reaches 20 or 25 depends on the instrument, the timeframe and the period setting.
• It ignores price level. Support, resistance, entries and targets come from price structure and other tools, such as Fibonacci retracement levels or moving averages.

FAQs

The Bottom Line

The ADX matters to traders in forex, stocks, futures and gold who need to tell trending markets from ranges. It works best as a filter alongside the +DI and -DI lines and the price chart, since it lags, shows no direction and does not forecast price. Test thresholds such as 20 and 25 against the instrument, timeframe and period setting you actually trade.