Trend Detector

Buy and sell signals are given when +DI and -DI cross. The time periods most commonly used in the complex formula are 10 or 14 days.

According to Wilder the DMI should be used with the ADX as a filter.

  • A rising ADX line means the market is trending and a better candidate for a trend-following system.
  • A falling ADX line indicates a non-trending market.
  • Some traders also look for an ADX greater than 20 or 25 to confirm that the market is trending. When the ADX line starts to drop from above the 40 level, that is an early sign that the trend is weakening. A rise back above 20 is often a sign of the start of a new trend.


Generally speaking, the two main buy and sell signals generated by DMI are as follows:

  • A buy signal is given when +DI crosses above the -DI line.
  • A sell signal is given when +DI crosses below the -DI line.

However, some refinements are suggested by experienced traders:

  • The crossing of DI lines only provides an early warning signal; other criteria must be fulfilled for the actual signal.
  • The ADX should be between the upper DI line and the lower one.
  • An ADX below 25 is a strong warning to avoid trading.

Wilder himself developed a refinement to take care of whipsawing (when the DI lines cross back and forth over a short period, providing unreliable signals). He called it his Extreme Point Rule.

The Extreme Point Rule is derived by noting the high or low point on the day when the +DI and the -DI cross one another. +DI determines the high or low point (if +DI is above -DI the Extreme Point is the high of the day, if +DI is below -DI, the Extreme Point is the low for the day).

The extreme point is then used for the actual buy or sell signal. For example, if the price once again rises above the Extreme Point price level you have a buy signal. If the price fails to rise above the extreme point, you should continue to stand aside. The converse holds true for sell signals.


An additional indicator, the average directional movement index rating (ADXR), was created by Wilder as a measuring tool for the strength of ADX. ADXR is the average of the current ADX and the ADX 14 days ago. ADXR is typically plotted alongside ADX on the same chart.



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