Does ADX above 25 mean buy?

No. Twenty-five is a common trend-strength heuristic, not a direction signal or a universally valid entry level.

Can ADX fall while a stock rises?

Yes. Price can continue rising while directional strength weakens under the ADX calculation.

What do +DI and −DI indicate?

They summarize positive and negative directional movement normalized by smoothed true range. Their relative positions describe direction, while ADX smooths the strength of the separation.

Glossary

What Is ADX? Trend Strength, +DI and −DI

ADX, the Average Directional Index, measures trend strength rather than bullish or bearish direction. It is derived from smoothed directional movement, with +DI and −DI describing the directional balance. A rising ADX can accompany a strong fall as well as a strong rally.

Strength is not direction

ADX belongs to Wilder's Directional Movement system. Changes in highs and lows produce positive and negative directional movement. These are smoothed and normalized using true range to form +DI and −DI.

The directional index is commonly expressed as 100 × |+DI − −DI| ÷ (+DI + −DI). ADX smooths that index. Flat-series and initialization conventions need explicit handling.

A practical interpretation

If −DI is above +DI while ADX rises, the reading can describe a strengthening downward trend. Treating every high-ADX reading as bullish is a category error.

Traders sometimes use ADX to separate trend-following research from range-trading research. For example, an ADX filter could restrict a moving-average strategy to stronger-trend conditions. Adding the filter is a new hypothesis that must be tested, not an automatic improvement.

Why values can disagree

Two charts can show different ADX values if they use different candles, periods, smoothing or warmup history. Write down all four before judging which is “correct.”

See ATR for true-range intuition and Supertrend for another indicator whose output should not be confused with a profitability guarantee.

Limitations

ADX is lagging and sensitive to lookback and initialization.
Thresholds such as 20 or 25 need testing for the instrument and timeframe.

Frequently asked questions

Does ADX above 25 mean buy?: No. Twenty-five is a common trend-strength heuristic, not a direction signal or a universally valid entry level.
Can ADX fall while a stock rises?: Yes. Price can continue rising while directional strength weakens under the ADX calculation.
What do +DI and −DI indicate?: They summarize positive and negative directional movement normalized by smoothed true range. Their relative positions describe direction, while ADX smooths the strength of the separation.

Last updated: 5 November 2026