AroonDown

Syntax

AroonDown[N]

Parameters

Formula

AroonDown = 100 * (N - BarsSinceLowestLow) / N

BarsSinceLowestLow counts how many bars have elapsed since the lowest low within the last N bars. A fresh low on the current bar gives 100. A low that occurred exactly N bars ago gives 0.

How it works

AroonDown answers a single question on every bar: how fresh is the most recent significant low. It scans the last N bars, locates the lowest low, and converts the elapsed time since that low into a percentage of the window.

The logic is time-based rather than price-based. It does not matter how deep the low was, only when it happened. A market grinding out new lows every few bars keeps AroonDown pinned near 100 even if each new low undercuts the previous one by a single tick.

The indicator is one half of the Aroon system. Its counterpart, AroonUp, applies the same measurement to the highest high. The two lines are usually read together: whichever line is dominant identifies the prevailing pressure, and crossovers between them mark potential changes in trend direction.

Examples

Example 1, Threshold signal from AroonDown (Indicator)

// Flag bars where downward pressure dominates the 20-bar window
N = 20
myAroonDown = AroonDown[N]
IF (myAroonDown > 50) THEN
  SIGNAL = 1
ELSE
  SIGNAL = -1
ENDIF
RETURN SIGNAL

Returns 1 while the lowest low of the last 20 bars occurred in the more recent half of the window, and -1 otherwise. A minimal building block for regime classification.

Example 2, Screening for fresh downtrends (ProScreener)

// Instruments making recent lows while highs grow stale
ad = AroonDown[25]
au = AroonUp[25]
SCREENER[ad > 70 AND au < 30](ad AS "AroonDown")

Returns instruments where the 25-bar low is recent and the 25-bar high is old, the standard Aroon definition of an established downtrend.

Example 3, Short entry on Aroon crossover (ProOrder)

// Sell short when downward pressure overtakes upward pressure
ad = AroonDown[25]
au = AroonUp[25]

IF NOT ShortOnMarket AND ad CROSSES OVER au AND ad > 70 THEN
  SELLSHORT 1 CONTRACT AT MARKET
ENDIF

IF ShortOnMarket AND au CROSSES OVER ad THEN
  EXITSHORT AT MARKET
ENDIF

Opens a short when AroonDown crosses above AroonUp with a strong reading, and covers when the relationship inverts. The threshold on ad filters weak crossovers that occur mid-range.

Interpretation

Readings are most useful relative to AroonUp. AroonDown above 70 while AroonUp sits below 30 is the classic downtrend signature. Both lines high at the same time indicates a volatile range where both a recent high and a recent low exist inside the window.

Common errors and gotchas

• No price argument. AroonDown takes only a period in square brackets. AroonDown[20](close) is invalid syntax, the calculation is always based on the low price series.
• High value means down, not up. The naming trips up new users. AroonDown near 100 is a bearish reading, it reports fresh lows. Reading it like an oscillator where high values are bullish inverts every signal.
• Time-based, not magnitude-based. One marginal new low resets the line to 100 regardless of how shallow the undercut was. In quiet markets this overstates the strength of a drift lower. Pairing with a volatility or trend-strength measure such as ADX gives context.
• Stair-step behaviour. Between new lows, the line declines in fixed increments of 100/N per bar. Crossover logic on very short periods generates dense clusters of signals because the line jumps in large steps.

Related instructions

• AroonUp, the companion line measuring bars since the highest high.
• ADX, trend-strength measure often combined with Aroon readings.
• DIminus, directional movement component for downward moves.
• DIplus, directional movement component for upward moves.
• LowestBars, returns the number of bars since the lowest value directly.
• HighestBars, returns the number of bars since the highest value.
• Lowest, the lowest value over a lookback window.
• Supertrend, trend-following level often used with directional indicators.