The Average Directional Index, or ADX, measures trend strength. It does not tell you whether price is going up or down.
That distinction matters. An ADX reading of 35 can appear during a rally or a sell-off. To read direction, you need the two lines plotted beside it:
| Line | What it tells you |
|---|---|
| ADX | How strong the current directional movement is |
| +DI | Positive directional movement relative to true range |
| -DI | Negative directional movement relative to true range |
I remember the three lines this way: DI shows the side. ADX shows the strength.
When +DI is above -DI, upward movement has been stronger over the lookback period. When -DI is above +DI, downward movement has been stronger. A rising ADX says that the gap between the two sides is becoming more persistent.
It still isn’t an instruction to buy or sell. ADX is most useful one step earlier, when deciding whether the market looks suitable for a trend-following idea at all.
How to read ADX
ADX runs from 0 to 100. Most readings stay well below the top of that scale.
| ADX reading | A practical interpretation |
|---|---|
| Below 20 | Directional movement is weak or mixed |
| 20 to 25 | A trend may be developing |
| 25 to 40 | Directional movement is established |
| Above 40 | Directional movement is strong; check price for extension |
These are reference zones, not market laws. An ADX of 24.8 and an ADX of 25.2 do not describe different worlds. What matters is the line’s direction, the relationship between +DI and -DI, and what price is doing around support, resistance, or a breakout level.
I pay more attention to these combinations:
- ADX rising, +DI above -DI: upward movement is becoming more dominant.
- ADX rising, -DI above +DI: downward movement is becoming more dominant.
- ADX falling: the current directional imbalance is fading. Price can still continue in the same direction.
- ADX low, DI lines crossing repeatedly: the market is probably rotating rather than trending.
The last two points prevent a lot of bad reads. Falling ADX is not automatically a reversal. And a DI crossover inside a low-ADX range is often just another turn inside the same range.
A high ADX can mean up or down
The AAPL examples below use the same ADX(14) calculation on daily candles.
On May 14, 2024, ADX moved above 25 with +DI at 40.0 and -DI at 14.4. Upward movement was dominant. AAPL closed at 187.43 and was 13.7% higher 20 trading sessions later.
On March 14, 2025, ADX was also near 25. This time -DI was 37.6 and +DI was 13.1. AAPL closed at 213.49 and was 7.2% lower 20 sessions later.
The ADX readings were similar. The direction came from the DI lines and the price chart.
This does not mean a move above 25 predicts what will happen over the next 20 sessions. It means the market had already developed a directional imbalance. ADX confirmed its strength after the move had started.
That delay is part of the indicator, not a defect in the calculation. ADX trades speed for confirmation.
What +DI and -DI actually measure
The directional lines are based on changes in each candle’s high and low.
For every new candle, the calculation compares:
- The current high with the previous high
- The current low with the previous low
- The candle’s true range, including gaps from the previous close
If the upward extension is larger, it contributes to positive directional movement. If the downward extension is larger, it contributes to negative directional movement. Wilder’s smoothing is then applied over a chosen period, usually 14 bars.
This produces +DI and -DI. The difference between them is converted into the Directional Index:
DX = 100 x |+DI - -DI| / (+DI + -DI)
ADX is a Wilder-smoothed average of DX.
You do not need to calculate this by hand to use the indicator. But the formula explains its behavior. ADX rises when one directional line pulls away from the other. It falls when the two move closer together.
Readings may differ slightly between platforms because candle data and the initial smoothing value are not always identical. A decimal-level mismatch does not change the interpretation.
Why DI crossovers fail in a range
A +DI/-DI crossover looks decisive on an indicator panel. In a sideways market, it may mean very little.
MSFT produced 14 DI crossovers between November 25, 2022, and January 31, 2023. Its average ADX during those 45 trading sessions was 13.7. The closing price finished almost where it started.
Every crossover identified the stronger side at that moment. The problem was persistence. Neither side held control for long enough to form a trend.
This is why I do not treat DI crosses as standalone entries. I first ask whether price is breaking out or still rotating between the same boundaries. Then I check whether ADX is rising from a low base. If the line stays weak while the DI lines keep swapping places, I leave the crossovers alone.
The order I use when reading ADX
1. Read price before the indicator
I start with the chart itself.
Is price making higher highs and higher lows? Is it making lower highs and lower lows? Are breakouts holding, or does price keep returning to the same area?
ADX cannot rescue a chart with no clear structure. It can only describe the directional movement already inside the candles.
2. Use DI to identify the dominant side
+DI above -DI supports an upward reading. -DI above +DI supports a downward one.
I care more about sustained separation than a single crossover. A brief cross followed by another cross is usually noise. A widening gap that agrees with price structure is more useful.
3. Use ADX as a regime filter
Low and flat ADX tells me that trend-following signals deserve more skepticism. Rising ADX tells me that directional movement is becoming more consistent. This is the same regime question behind trend following versus mean reversion: is price expanding in one direction or rotating inside a range?
I do not require 25 in every market and on every timeframe. Some instruments trend cleanly while ADX is in the low twenties. Others produce short spikes above 25 that fade quickly. The threshold needs to make sense for the instrument and setup being tested.
4. Build the trade around price
ADX does not provide a stop, an invalidation level, or a profit target.
Those decisions still come from price. A breakout level, swing low, swing high, support zone, or resistance zone can define where the idea stops making sense. The indicator only helps decide whether the environment favors continuation.
Rising ADX versus falling ADX
The slope often tells you more than the headline number.
Suppose ADX is at 38 and falling. The trend may still be intact, but the directional gap is narrowing. That can happen during a pause, a pullback, or the early stage of a range.
Now suppose ADX is at 18 and rising. The market is not yet strongly directional, but conditions are changing. If price has just broken a well-tested level and the DI lines agree, that may be more useful than a late reading above 40.
There is no contradiction here. The number describes strength. The slope describes whether that strength is increasing or decreasing.
ADX settings and timeframes
The standard period is 14. It means 14 candles, not 14 days.
On a daily chart, the input uses daily candles. On a 15-minute chart, it uses 15-minute candles. The same setting can behave differently because market noise and session structure change with the timeframe.
- Shorter periods, such as 7 or 10, react faster but produce more abrupt changes.
- The standard 14-period setting is a reasonable place to learn the indicator.
- Longer periods, such as 20 or 28, move more slowly and filter more short-lived changes.
I would not change the period just to make an old trade look better. Pick a setting, test it across many examples, and keep the definition consistent.
Common ADX mistakes
Treating high ADX as bullish
ADX has no bullish or bearish direction. Check the DI lines and price.
Buying the moment ADX crosses 25
The cross confirms that directional movement has strengthened. It does not tell you whether the entry price, stop distance, or remaining upside makes sense.
Calling every DI crossover a reversal
DI lines can cross repeatedly in a range. The MSFT example showed 14 crosses with almost no net movement.
Assuming falling ADX means price must reverse
A trend can continue at a slower pace while ADX falls. Look for an actual break in price structure before calling a reversal.
Comparing readings across unrelated timeframes
ADX(14) on a five-minute chart and ADX(14) on a daily chart summarize different market behavior. The number may match while the context does not.
The rule I keep
Price establishes the direction. DI shows which side has been stronger. ADX shows whether that advantage is persistent.
I do not enter because ADX crossed a number. I use it to decide whether a trend-following setup belongs in the current market at all.
