ADX: How to Measure Trend Strength, Not Direction
ADX answers a question other indicators sidestep: is there any movement at all, or is the market marking time? It shows no direction — it rises in a rally and in a decline alike.
The ADX indicator: how it is calculated
The indicator is built from two directional lines, +DI and −DI, each measuring the share of movement in its own direction. ADX itself is a smoothed measure of the gap between them, so it rises when one side dominates steadily and falls when they intertwine. A reading above 25 is conventionally taken as a sign of a trend, below 20 as its absence.
How many signals it produces on real data
- Rule tested: ADX(14) above 25 — the move has force
- State changes over the sample: 13 — about 6.7 a year
- Share of bars in the signal state: 32.1%
Measured across 518 daily bars for each of 12 currency pairs. This measures frequency, not profitability: it shows how many decisions the tool demands of a trader. The data is public and the calculation is reproduced by a script in the repository.
How it differs from similar tools
The key difference from other indicators is that ADX gives no entry signal. It gives permission or prohibition: at a low reading, trend rules switch off because there is nothing for them to work on. Direction is then taken from +DI and −DI or from price structure.
How to apply it
Its most valuable use is as a regime filter. The measurement shows ADX above 25 occurred on only a third of days: which means for two thirds of the time trend strategies trade in conditions they were not designed for. Switching them off for that period does not improve the signals — it removes ones that were false to begin with.
Common mistakes
The main mistake is reading a rising ADX as a buy signal. It rises in declines too, and a trader who bought on rising ADX in a downtrend got exactly what the indicator was showing. The second is expecting precise timing from ADX: it is smoothed and lags, so it confirms the force of a move after it has already begun.
This material is for educational purposes and is not individual investment advice.
Frequently asked questions
What does the ADX indicator show?
The strength of a move without its direction. It rises in both uptrends and downtrends, and a low reading means the absence of a trend as such.
What does ADX above 25 mean?
That the move has force and trend approaches apply. In our measurement across 12 pairs such a reading occurred on only 32% of days.
Can you determine direction from ADX?
No — the +DI and −DI lines or price structure serve that purpose. ADX itself measures strength only.
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