Directional Movement Index (DMI)¶
The Directional Movement Index (DMI) is a trend-following indicator developed by J. Welles Wilder that measures which direction price is moving by comparing upward and downward directional movement. It plots two lines — the positive directional indicator (+DI) and the negative directional indicator (-DI) — to show whether buyers or sellers control the tape. The DMI is the engine inside the Average Directional Index (ADX), which smooths the difference between the two DI lines to quantify trend strength.
HOW IT WORKS¶
The DMI is calculated over a default 14-period lookback in four steps. First, +DM captures the excess of the current high over the prior high (if positive and larger than the down move), and -DM captures the excess of the prior low under the current low (if positive and larger than the up move). Both are then smoothed alongside True Range using Wilder smoothing. Finally, +DI = 100 × (smoothed +DM / smoothed TR) and -DI = 100 × (smoothed -DM / smoothed TR), producing two lines that oscillate between 0 and 100. When +DI sits above -DI, buyers control the trend; when -DI sits above +DI, sellers do. A cross between the two lines signals a potential trend change. Readings above 25 on the dominant line suggest a firm trend; readings below 20 on both lines indicate a directionless market.
IN TAPEBOARD¶
Traders use the DMI in the Tapeboard terminal primarily as a trend entry and exit trigger, taking long signals when +DI crosses above -DI and exit signals on the reverse cross. The standard workflow pairs the DI cross with ADX above 20–25 to confirm a real trend is behind the signal and filter out whipsaw crosses in flat markets. The DMI also functions as a regime gate: traders disable mean-reversion setups when one DI line dominates and enable them only when both lines sit below 20. Use the live scanner to screen for stocks with a wide +DI/-DI spread, indicating strong directional trends in real time.