ADX Indicator: What Is Average Directional Index and How Does It Work?

The ADX indicator helps traders assess whether a market has a meaningful trend and how strong that trend is. It does not independently show whether prices are moving up or down.

Developed by technical analyst J. Welles Wilder Jr., ADX forms part of the Directional Movement System. It is generally displayed with the Positive Directional Indicator (+DI) and Negative Directional Indicator (−DI), which add information about price direction.

This article explains the average directional index, its formula, components, settings and interpretation, along with its advantages and limitations.

What is the average directional index?

The average directional index, or ADX, is a technical analysis indicator that measures the strength of a price trend over a selected period. Its value ranges from 0 to 100.

ADX is non-directional. It can rise during a strong uptrend or downtrend because it measures the intensity of directional movement rather than its direction.

Direction is assessed using the accompanying +DI and −DI lines:

• +DI represents positive or upward directional movement.
• −DI represents negative or downward directional movement.
• ADX measures the strength of the directional movement reflected by these lines.

A rising ADX with +DI above −DI can indicate strengthening upward movement. If ADX is rising while −DI is above +DI, downward movement is gaining strength.

Understanding ADX trend strength

ADX readings are commonly interpreted using broad reference ranges:

These ranges are guidelines, not universal trading rules. Their relevance can vary across assets, timeframes and market conditions.

The movement of the ADX line also provides useful context:

• Rising ADX: Directional strength is increasing.
• Falling ADX: Directional strength is decreasing.
• Flat ADX: Trend strength is relatively stable.

A falling ADX does not automatically signal a reversal. The price may continue in the same direction more slowly or move into consolidation. Likewise, a reading above 25 is not automatically a buy signal because ADX does not establish direction.

ADX levels are interpretive reference points and may behave differently across assets and timeframes.

The figures shown are for illustrative purpose only.

Components of ADX

The Directional Movement System has three principal components:

ADX line

The ADX line measures trend strength. It does not identify whether the prevailing movement is upward or downward.

Positive Directional Indicator (+DI)

+DI measures upward directional movement relative to the asset’s true range.

Negative Directional Indicator (−DI)

−DI measures downward directional movement relative to the true range.

How to interpret +DI and −DI signals

The relationship between the two directional indicators helps establish direction:

• +DI above −DI: Upward directional movement is dominant.
• −DI above +DI: Downward directional movement is dominant.
• +DI crossing above −DI: Upward movement may be gaining control.
• −DI crossing above +DI: Downward movement may be gaining control.

A widening gap between +DI and −DI indicates growing dominance in one direction. A narrowing gap suggests that this dominance is weakening.

DI crossovers can occur frequently in range-bound markets. A crossover is therefore more informative when supported by a rising ADX and corresponding price behaviour.

ADX indicator formula and calculation

The ADX indicator formula measures trend strength using true range, positive and negative directional movement, and Wilder’s smoothing method. The standard calculation generally uses 14 periods.

Step 1: Calculate true range

True range (TR) captures the current price range and any gap from the previous closing price.

Calculate these three values:

• Current high minus current low
• Absolute value of current high minus previous close
• Absolute value of current low minus previous close

Formula:

• TR = Highest of [(Current high − Current low), |Current high − Previous close|, |Current low − Previous close|]

The vertical bars indicate that the difference is treated as a positive value.

Step 2: Calculate directional movement

First, calculate the upward and downward moves.

Formulas:

• Up move = Current high − Previous high
• Down move = Previous low − Current low

The Positive Directional Movement (+DM) and Negative Directional Movement (−DM) are then determined as follows:

• If the up move is positive and greater than the down move, +DM equals the up move. Otherwise, +DM is zero.
• If the down move is positive and greater than the up move, −DM equals the down move. Otherwise, −DM is zero.

Only the larger qualifying directional movement is counted for a period. If neither move meets these conditions, both +DM and −DM are zero.

Step 3: Smooth TR, +DM and −DM

TR, +DM and −DM are smoothed over the selected lookback period. In the standard calculation, n equals 14.

The first smoothed value is the sum of the first n values.

Formula:

• Initial smoothed value = Sum of the first n values

Each subsequent value is calculated using Wilder’s smoothing method.

Formula:

• Current smoothed value = Previous smoothed value − (Previous smoothed value / n) + Current value

This calculation is applied separately to TR, +DM and −DM.

Step 4: Calculate +DI and −DI

The smoothed directional movements are expressed as percentages of the smoothed true range.

Formulas:

• +DI = 100 x (Smoothed +DM / Smoothed TR)
• −DI = 100 x (Smoothed −DM / Smoothed TR)

+DI represents the strength of upward directional movement, while −DI represents the strength of downward directional movement.

Step 5: Calculate the Directional Index

The Directional Index (DX) measures the difference between +DI and −DI relative to their combined value.

Formula:

• DX = 100 x [Absolute value of (+DI − −DI) / (+DI + −DI)]

In this formula, −DI is the name of the Negative Directional Indicator rather than a negative number. The formula can therefore be read as:

• DX = 100 x [Absolute difference between +DI and −DI / Sum of +DI and −DI]

The absolute difference removes direction from the result. Strong upward and downward price movements can therefore both produce a high DX reading.

Step 6: Calculate the initial ADX

The first ADX value is the average of the first n DX values.

Formula:

• Initial ADX = Sum of the first n DX values / n

For a 14-period setting:

• Initial ADX = Sum of the first 14 DX values / 14

Step 7: Calculate subsequent ADX values

Later ADX readings are calculated using Wilder’s smoothing method.

Formula:

• Current ADX = [(Previous ADX x (n − 1)) + Current DX] / n

For a 14-period setting:

• Current ADX = [(Previous ADX x 13) + Current DX] / 14

Because the calculation applies smoothing at several stages, ADX confirms changes in trend strength with a delay. Charting platforms generally perform these calculations automatically.

Indicator values may differ slightly across platforms because of differences in price data, rounding, initial values or smoothing conventions.

How to read ADX

ADX should be interpreted using its level and direction together with the relative positions of +DI and −DI:

A turn in the ADX line should be treated as information about trend strength, not as an automatic instruction to enter or exit a trade.

ADX trading strategy

ADX can help traders distinguish between trending and range-bound conditions, but it does not provide a complete trading strategy on its own.

Confirming an existing trend

A trader may first identify a trend from the price chart and then use ADX to assess its strength. For example, upward price structure, +DI above −DI and a rising ADX may collectively support the presence of strengthening upward movement.

For a downtrend, a trader may look for falling price structure, −DI above +DI and a rising ADX.

Assessing a breakout

A breakout accompanied by a rising ADX may indicate increasing directional strength. Since ADX can respond after the price has begun moving, volume and a sustained close beyond the relevant price level can provide additional context.

Identifying weak trend conditions

A persistently low ADX may indicate that the market lacks sustained directional movement. Trend-following signals, particularly frequent DI crossovers, may be less useful under such conditions.

Monitoring a developing trend

A rising ADX indicates strengthening directional movement. If ADX begins to fall, the trend is losing strength, but this does not confirm that the price will reverse.

These examples are illustrative and do not constitute trading recommendations. Technical indicators cannot assure profitable outcomes.

Common ADX settings

The standard ADX setting is 14 periods, based on Wilder’s original methodology. A period corresponds to the interval used on the chart:

• On a daily chart, 14 periods represent 14 trading sessions.
• On an hourly chart, they represent 14 hourly candles.
• On a weekly chart, they represent 14 weeks.

Different settings change the indicator’s sensitivity:

No setting is suitable for every asset or timeframe. Any adjustment should be tested across trending, volatile and range-bound periods.

Advantages of ADX

The average directional index offers the following advantages:

Objective trend-strength measurement

ADX converts directional price movement into a numerical reading that can be compared across periods.

Separation of strength and direction

The ADX line measures strength, while +DI and −DI indicate which direction is dominant.

Use across markets and timeframes

The indicator can be applied to stocks, indices, commodities, currencies and other traded instruments on intraday or longer-term charts.

Identification of market conditions

ADX can help distinguish stronger trending phases from weaker or range-bound periods.

Compatibility with other tools

It can add trend-strength context to analysis based on price structure, volume, moving averages, support and resistance, or momentum indicators.

Strategic insights for using ADX in trading

The following practices can support more balanced ADX interpretation:

• Read ADX with +DI and −DI rather than treating the ADX line as a directional signal.
• Assess the direction of the ADX line instead of relying only on a single numerical reading.
• Confirm indicator signals against price structure, support, resistance and trading volume.
• Be cautious with repeated DI crossovers when ADX is low.
• Match the setting to the asset and timeframe being analysed.
• Test the approach across different market conditions and account for transaction costs.
• Use defined position-sizing and risk-management rules rather than relying on ADX alone.

Limitations of ADX

ADX also has important limitations:

Lagging signals

ADX is calculated from historical prices and uses smoothing. It may confirm a trend after part of the move has already occurred.

No independent directional signal

A high ADX does not reveal whether prices are rising or falling. Direction must be assessed using the DI lines or the price chart.

False crossovers

+DI and −DI can cross repeatedly in volatile or range-bound markets, producing misleading signals.

Variable threshold relevance

A reading that is significant for one asset or timeframe may be less useful for another. Standard thresholds should be treated as guidelines.

No reversal prediction

A falling ADX indicates decreasing trend strength, not necessarily an approaching reversal.

No fundamental analysis

ADX evaluates price movement only. It does not consider valuation, earnings, economic conditions or business quality.

Conclusion

The ADX indicator measures the strength of directional price movement, while +DI and −DI help identify whether upward or downward movement is dominant. Together, these indicators can help traders distinguish a trending market from one with weak directional movement.

ADX is most useful as a confirmation tool. Since it relies on historical price data and can generate misleading signals in range-bound conditions, it should be interpreted with price analysis, other relevant indicators and appropriate risk controls.

FAQs

What does the ADX indicator tell you?

The ADX indicator measures the strength of a price trend. It does not independently show the direction, which is assessed using +DI, −DI and the price chart.

What is a good ADX value for trading?

An ADX reading above 25 is commonly viewed as indicating a more established trend, while a reading below 20 often reflects weak directional movement. These are reference levels rather than universal trading rules.

Is ADX a leading or lagging indicator?

ADX is a lagging indicator because it uses historical price data and smoothing. It confirms trend strength after directional movement has begun rather than predicting a trend.

How reliable is the ADX indicator?

ADX can provide useful information about trend strength, but it should not be used as a standalone trading signal. Its usefulness depends on the market, timeframe, setting and supporting price evidence.

What is the default setting for ADX?

The standard ADX setting is 14 periods, based on Wilder’s original methodology. Shorter settings respond faster, while longer settings produce smoother readings.

Does a high ADX mean the price will rise?

No. A high ADX indicates strong directional movement, which can occur during either an uptrend or a downtrend.

What does a falling ADX mean?

A falling ADX means that trend strength is decreasing. It does not confirm that the trend has ended or that a price reversal will occur.

Can ADX be used for intraday trading?

Yes. ADX can be applied to intraday charts, although shorter timeframes may produce more noise and frequent changes in the DI lines.

What is the difference between ADX and ATR?

ADX measures trend strength, while Average True Range measures volatility. Both use true range in their calculations but evaluate different aspects of price behaviour.

What is the difference between ADX and RSI?

ADX measures trend strength. The Relative Strength Index measures price momentum and is commonly used to assess whether recent gains or losses have become relatively extended.

Can ADX identify a trend reversal?

No. ADX can show that a trend is weakening, but confirmation of a reversal requires evidence from price action or other analytical tools.

Why does ADX rise during a downtrend?

ADX rises during a strong downtrend because it measures the strength of directional movement rather than its direction. In this situation, −DI would generally be above +DI.