ADX (Average Directional)

This calculator performs one update of J. Welles Wilder’s Average Directional Index: from the current +DI and −DI and the previous ADX it returns the new ADX, the raw DX and a plain-language read on trend strength.

How the calculation works

Wilder introduced ADX in New Concepts in Technical Trading Systems (1978). The first step is the directional index, DX = |+DI − −DI| ÷ (+DI + −DI) × 100. The more one side dominates the other, the higher DX.

DX is then smoothed with Wilder’s method: ADX = (previous ADX × (N − 1) + DX) ÷ N, an exponential average with weight 1/N. The standard period is 14. Enter the current bar’s +DI and −DI (from your charting platform), the prior ADX and N.

The output shows DX, the new ADX, a strength label — ADX ≥ 25 trending, 20–25 weak trend, below 20 no trend — and direction: +DI above −DI signals upward pressure, otherwise downward.

Worked example

Defaults: +DI = 30, −DI = 15, previous ADX = 22, N = 14. DX = |30 − 15| ÷ 45 × 100 = 33.33. ADX = (22 × 13 + 33.33) ÷ 14 ≈ 22.81, a weak-trend reading, with +DI above −DI pointing up. If DX stays around 33 for a few more bars, ADX will keep climbing toward 25.

Things to keep in mind

• ADX measures strength, not direction. A rising ADX with −DI on top means a strengthening downtrend.
• Because of double smoothing, ADX lags. A turn down from high levels usually signals a slowing trend, not necessarily a reversal.
• The very first ADX is the simple average of the first N DX values; after that the recursive formula used here applies.
• The 20 and 25 thresholds are conventions, not laws — traders tune them by market and timeframe. Nothing here is investment advice.