Aroon Indicator¶
OVERVIEW¶
The Aroon indicator, introduced by Tushar Chande in 1995, measures the time elapsed since the highest high and lowest low within a lookback window. It plots two lines — Aroon Up and Aroon Down — that oscillate between 0 and 100. Aroon Up tracks the freshness of new highs; Aroon Down tracks the freshness of new lows. The name comes from the Sanskrit word for "dawn's early light," reflecting Chande's intent to detect new trends early, before momentum oscillators confirm them.
| Line | What It Tracks |
|---|---|
| Aroon Up | Recency of new highs within the lookback window |
| Aroon Down | Recency of new lows within the lookback window |
| Aroon Oscillator | Aroon Up minus Aroon Down (range: −100 to +100) |
HOW IT IS CALCULATED¶
For a lookback period of n bars (default 25):
Aroon Up = ((n − bars since n-period high) / n) × 100
Aroon Down = ((n − bars since n-period low) / n) × 100
Aroon Oscillator = Aroon Up − Aroon Down
If the highest high occurred today, "bars since high" = 0 and Aroon Up = 100. If it occurred 25 bars ago, Aroon Up = 0. Each line is independent — both can read high simultaneously when a stock makes a new high and a new low within the same window, signaling expanded range rather than trend.
Standard signal thresholds:
| Market Condition | Aroon Up | Aroon Down |
|---|---|---|
| Strong uptrend | > 70 | < 30 |
| Strong downtrend | < 30 | > 70 |
| Consolidation | < 50 | < 50 |
| Trend change (bullish) | Crosses above Aroon Down | — |
| Trend change (bearish) | Crosses below Aroon Down | — |
WORKED EXAMPLE¶
Suppose NVDA is in the middle of a rally. Over the past 25 sessions:
| Measurement | Value | Calculation |
|---|---|---|
| Highest high | 3 bars ago | ((25 − 3) / 25) × 100 = 88 |
| Lowest low | 22 bars ago | ((25 − 22) / 25) × 100 = 12 |
| Aroon Oscillator | — | 88 − 12 = +76 |
The reading confirms a strong uptrend: new highs are recent, new lows are stale, and the oscillator sits near its upper bound. A swing trader using Aroon as a filter would maintain longs only while the oscillator stays positive and exit on a cross back below zero.
Contrast with a ranging market: if NVDA's highest high was 11 bars ago and lowest low was 9 bars ago, Aroon Up = 56 and Aroon Down = 64 — both lines below 70, oscillator near zero. The chart is choppy and trend-following strategies will whipsaw.
WHEN TRADERS USE IT¶
The Aroon indicator is used as a regime filter — to determine whether the market is trending or chopping before applying a trend strategy. Pair it with a momentum oscillator like RSI or MACD to avoid taking overbought signals during a strong trend. Quantitative systems use the Aroon Oscillator as a position-sizing input, scaling exposure in proportion to oscillator magnitude.
LIMITATIONS AND MISCONCEPTIONS¶
Aroon is a timing indicator, not a magnitude indicator. Two stocks with identical Aroon readings can have radically different volatility and trend depth — the indicator measures recency of extremes, not size of the move. The 25-period default lags fast reversals; cutting to 14 periods produces more signals but more whipsaws. Aroon also generates false signals in low-volume drift markets where a single tick can create a new "high" inside the window. Use Aroon alongside Average True Range to filter out signals from low-range periods.
| Limitation | Detail |
|---|---|
| No magnitude measurement | Measures recency of extremes, not size of the move |
| Lag on fast reversals | 25-period default may miss sharp turns |
| False signals in thin markets | A single tick can create a new high in low-volume drift conditions |
| Whipsaw risk | Shorter periods increase signal frequency and noise |