Indicators · Intermediate

ADX And Measuring Trend Strength

ADX answers one question and refuses the other. It tells you whether a trend is worth following, never which way to follow it.

Last reviewed 15 September 2026 by the MarketPro research desk · Editorial policy

In short

The Average Directional Index measures trend strength on a 0 to 100 scale without indicating direction, because the formula discards the sign of the movement it measures. Below 20 suggests range conditions in which trend tools underperform, and above 25 and rising suggests a trend is underway. Direction comes from the +DI and -DI lines plotted alongside it, which show whether upward or downward movement currently dominates.

What to remember

ADX is built from magnitude only. The calculation takes the absolute difference between the DI lines, so sign is discarded before the reading is produced.
Slope beats level. An ADX of 22 rising from 14 says more than an ADX of 30 that has been flat for three days.
Filtering out signals that fire below 20 removes the trades taken in conditions the system was never built for.
A falling ADX is ambiguous. It cannot tell a trend that is ending from a strong trend that is resting.

Lesson 10 of 22 in Trading indicators

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Most losing trades are not bad trades. They are good trades taken in the wrong conditions, a breakout rule applied to a range or a fade applied to a trend. ADX exists to answer that question and only that question: is there a trend here worth following, or is there not? It is silent on which way that trend points, because the calculation takes the absolute difference between its two directional lines and throws the sign away before it produces a number.

Directional movement before it is smoothed

The raw input is simple. For each bar, compare the high to the previous high and the low to the previous low. If the high has risen by more than the low has fallen, the bar has positive directional movement, and its size is the rise in the high rather than the difference between the two comparisons. If the reverse, it has negative directional movement. Only one of the two can be non-zero on a bar, and an inside bar has neither.

Those movements are summed and smoothed over 14 periods, divided by ATR to express them as percentages, and plotted as +DI and -DI. ADX itself is the smoothed absolute difference between the two DI lines, divided by their sum. That double smoothing is why ADX is slow, and why it can still be rising after a trend has stopped extending.

A quarter of crossovers, sorted by ADX

Here is the arithmetic that makes ADX worth having. Suppose a 20/50 moving average crossover system on a 4-hour chart produces 30 signals in a quarter. Sort them by the ADX reading at the moment of the cross.

ADX at the signal	Signals	What the condition was
Below 20	17	Range, the averages sitting on top of each other
20 to 25	6	Ambiguous, direction not settled
Above 25 and rising	7	A trend actually underway

More than half the signals arrived in conditions the system was never designed for. Applying a single filter, no ADX below 20, removes 17 trades. If each of those cost the spread plus an average 9 pips of adverse movement before the flip, on 1 per cent risk per trade that is a meaningful share of the quarter's drawdown spent on correctly executing the wrong playbook. Nothing about the entry logic needed changing. The switch was never checked.

The same sorting works in reverse. A mean-reversion rule that fades extremes belongs in the 17 signals below 20 and is actively dangerous in the 7 above 25, where fading a move means selling into demand that has just demonstrated it can absorb everything offered to it. Both rule sets are perfectly sound. The regime decides which one is currently correct, and reading the regime by feel is how a run of small gains turns into one large loss.

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Rising at 22 beats flat at 30

The conventional levels are below 20 for a weak or absent trend, above 25 for a trend worth following, and above 40 for a strong one. Those are conventions, and the number alone is the less informative half of the reading.

Slope carries more. An ADX of 22 that has climbed from 14 over the last eight bars describes a trend that is forming. An ADX of 30 that has been flat for three days describes a trend that has stopped strengthening, which is a different and less attractive proposition. A reading is a snapshot of something that only means anything as a direction of travel.

Watch the DI lines alongside it for the same reason. ADX is derived from the gap between +DI and -DI, so a rising ADX is always a statement that one side is pulling away from the other. When the two DI lines are winding around each other within a point or two, ADX has nothing to measure and any reading it produces is noise dressed as a number.

A falling ADX is two different stories

It can mean the trend is ending, as the DI lines converge and movement becomes two-sided.
It can equally mean a strong trend is resting. A consolidation inside a trend pulls ADX down without changing the trend at all.
The reading cannot distinguish them, which is why a falling ADX is a reason to stop adding rather than a reason to reverse.
High readings arrive late. Above 40 usually coincides with the mature part of a move, which is when joining offers the worst reward for the risk taken.

One filter, written into the plan before the session

The way to use this is as a switch rather than a signal. Write two sets of rules, one for trending conditions and one for ranging, and let ADX decide which set is live today. In a trend, targets sit further out and trailing a stop is sensible. In a range, the target is bounded by the range and holding for more is how a winner becomes a loser.

Then pair it with the DI lines for direction. A +DI above -DI with ADX above 25 and rising is a combined statement: there is a trend and it points up. The entry still comes from a level or from structure, because a DI crossover on its own is frequent and unremarkable. Stop distance follows volatility, size follows the stop, and both are settled on the position size calculator before you commit. If you want to see what a quarter of trades in the wrong regime does to an account, the drawdown calculator makes it concrete, and the risk management guide explains why shallow drawdowns are the whole game.

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Written and reviewed by the MarketPro research desk

MarketPro is a trading-signal and trading-education app operated by Harajuku Holdings LTD (Cyprus). Our signal desk publishes and tracks every trade idea in-app, and every page here is checked against the app's live behaviour before publishing. Last reviewed 15 September 2026. How we produce signals and content · About MarketPro

FAQ

ADX And Measuring Trend Strength: questions

What ADX level indicates a strong trend?

Readings above 25 are conventionally treated as evidence of a trend worth following and above 40 as a strong one, while below 20 suggests range conditions. These are conventions rather than fixed thresholds, and the direction of travel matters more than the exact value. An ADX rising through 22 often carries more information than a flat reading at 30.

Does ADX tell you whether to buy or sell?

No. ADX measures only how decisively one side is outpacing the other, and the formula strips the sign before producing its number, so a strong advance and a strong decline are indistinguishable on the ADX line alone. The +DI and -DI lines that accompany it are what indicate which side currently dominates. Using ADX by itself to choose a direction misreads what the calculation produces.

How do you use ADX as a filter?

The common approach is to write two sets of rules, one for trending conditions and one for ranging, and let the ADX reading decide which applies. Trend-following entries are only taken when ADX is above the threshold and rising, and mean-reversion entries only when it is low. That turns ADX into a regime switch rather than a trade signal.

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