Bollinger Band Width explained

Volatility

What Bollinger Band Width measures

BB Width measures the width of Bollinger Bands as a percentage of the middle band, providing a pure volatility metric. When the bands are extremely narrow (BB Width near multi-period lows), the market is in a low-volatility squeeze that historically precedes significant directional moves. It removes the absolute price context and isolates volatility.

How Bollinger Band Width readings are interpreted

Very low BB Width = volatility compression = breakout incoming. Very high BB Width = peak volatility = potential exhaustion/reversal. The squeeze signal is triggered when BB Width reaches its lowest point in 125+ days. The direction of the breakout needs to be determined by price action or other indicators.

Conventional Bollinger Band Width levels

BB Width at a 6-month low (the squeeze): volatility is compressed, which often precedes expansion
BB Width expanding rapidly: volatility is expanding, conventionally read as a move underway
BB Width at 6-month high: volatility peak, potential trend exhaustion
BB Width falling from high levels: volatility declining, market calming
1.5% width: typical 'squeeze' threshold for daily stock charts

Where Bollinger Band Width works, and where it does not

The volatility compression breakout setup works in all market regimes. It's one of the most reliable technical patterns because it doesn't predict direction — it just identifies that a large move is coming. After identifying a squeeze, use price action, MACD, or volume to determine direction.

Indicators commonly read alongside Bollinger Band Width

ATR: Both confirming low volatility = very strong squeeze signal
MACD: Squeeze setup + MACD crossing zero = direction confirmed for breakout
Volume: Squeeze + volume spike in a direction = breakout confirmed

Known limitations of Bollinger Band Width

BB Width alone cannot tell you which direction the breakout will go
After earnings, BB Width expands rapidly and then compresses — the post-earnings squeeze is different from a normal squeeze
Very short-period BB (less than 10 periods) makes BB Width too noisy to be useful

Bollinger Band Width in practice

A new 6-month low in BB Width is the conventional trigger for adding a name to a watchlist
It is usually paired with a directional indicator — BB Width turning up alongside an RSI 50 cross in the breakout direction
The squeeze more often resolves in the direction of the most recent prior trend
Stop distances of 1× ATR outside the opposite band are a common reference in breakout approaches

Other volatility indicators

Normalized ATR
Keltner Channel
Donchian Channel
Opening Range (ORB)

Testing ideas built on Bollinger Band Width

A reading of Bollinger Band Width can be written as an exact rule and checked against historical data — as a full strategy with entries, exits and costs, or as a single condition and what followed it:

How to backtest a trading strategy without code
Event analysis: what follows a market event

Plot it yourself. Add this indicator to a chart, change every parameter and watch the line move, then backtest how the rule would have behaved on historical data — free on the S&P 500 ETF, no card.

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This is reference material, not advice. It describes what each indicator measures and how its readings are conventionally interpreted. Nothing here is a recommendation to buy or sell anything, and no indicator predicts future prices. GU Analyser is an analytical tool — no money is ever traded here.