ADX: Trend Strength and Directional Movement

Keep strength and direction separate

The directional-movement family contains +DI, −DI and ADX. MetaQuotes describes these separate lines. ADX can rise during either an upward or downward trend. Reading an increase in ADX as a buy signal confuses the strength summary with the directional components from which it is constructed.

A common Wilder-style calculation compares the increase in successive highs with the decrease in successive lows. Positive directional movement retains the upward change only when it is positive and greater than the downward change; negative directional movement uses the reverse rule. Ties and inside bars require explicit handling, commonly contributing zero directional movement.

Follow one hypothetical update

Suppose the previous high and low were 105 and 100. The new high and low are 108 and 101. Upward movement is 3, while downward movement is −1, so the example contributes +DM of 3 and −DM of zero. With a previous close of 104, true range is the maximum of 7, 4 and 3, or 7.

After smoothing directional movement and true range over a declared period, assume +DI equals 30 and −DI equals 10. DX is 100 × absolute(30 − 10) / (30 + 10) = 50. ADX smooths that DX series rather than simply copying the latest difference.

If an initialized 14-period ADX is 25, the next Wilder-style update with DX of 50 is (13 × 25 + 50) / 14 = 26.7857. Swapping +DI and −DI to 10 and 30 leaves DX at 50. This shows directly why the strength calculation is insensitive to which direction dominates.

Initialization changes early results

There are multiple smoothing stages and a warm-up interval. A short chart history may produce a different early series from a platform loaded with years of data. MetaQuotes exposes both standard ADX and Wilder-specific indicator interfaces; implementation names and defaults should therefore be checked rather than assumed identical.

If both directional components are zero, the DX denominator is zero. A program needs a documented fallback or missing-value policy. A quiet or flat series should not accidentally create an infinite strength reading because of unchecked arithmetic.

Interpret thresholds as a hypothesis

Common threshold labels are conventions, not universal boundaries between tradable and untradable markets. Smoothing can leave ADX elevated after the underlying directional move has slowed. It can also keep ADX low near the beginning of a move that later looks obvious on a historical chart.

Inspect true-range inputs, then compare a fully specified crossover rule with and without the same ADX condition. Use an untouched evaluation set for that comparison. A filter that improves one selected chart is not evidence of a durable improvement across instruments or periods.