What Is Bollinger Bands? Calculation, Squeeze Breakouts & Trading Rules

Direct Answer: What Is Bollinger Bands?

Bollinger Bands are a technical analysis tool created by John Bollinger in the 1980s that plots dynamic volatility bands around an asset's price. The indicator consists of a 20-period simple moving average (middle band) and two outer bands placed two standard deviations above and below it, expanding during volatile periods and contracting during consolidations.

How Bollinger Bands Are Calculated

Unlike fixed-percentage envelopes, Bollinger Bands adjust dynamically to market conditions using statistical standard deviation (σ):

Middle Band:
Middle Band = 20-Period Simple Moving Average (SMA)

Upper Band:
Upper Band = 20-Period SMA + (2.0 × 20-Period Standard Deviation)

Lower Band:
Lower Band = 20-Period SMA - (2.0 × 20-Period Standard Deviation)

Under Gaussian distribution principles, approximately 88% to 90% of price action takes place within two standard deviations of the mean. Touching the outer bands indicates an overextended price relative to the 20-period baseline.

The Bollinger Band Squeeze & The BandWidth Formula

Markets alternate between periods of low volatility (consolidation) and high volatility (trending expansion). The Bollinger Band Squeeze is the visual representation of this compression cycle:

The BandWidth Metric

BandWidth = (Upper Band - Lower Band) / Middle Band

When BandWidth drops to 6-month or 12-month historical lows, the bands tighten around price candles like a coiled spring. This signals that volatility has dried up and a powerful breakout move is building.

Critical Risk Rule: A squeeze does not forecast breakout direction. Expecting an upward breakout simply because a stock is consolidating is a frequent error. A squeeze can break down just as easily as it can break up.

Walking the Bands vs Mean Reversion

Traders must distinguish between two mutually exclusive market regimes when using Bollinger Bands:

1. Ranging Regime (Mean Reversion)

In horizontal, sideways markets, the outer bands act as dynamic support and resistance. Prices tag the upper band, find supply, and mean-revert to the 20 SMA middle band. Touching the lower band prompts an oversold bounce back toward the median.

2. Trending Regime ("Walking the Bands")

During powerful structural breakouts, prices "walk the band." In an aggressive bull run, price candles continually touch, pierce, and ride along the upper band for 10 to 20 consecutive sessions. Shorting simply because price touches the upper band during a trending expansion leads to large losses.

Head-Fake Traps & Breakout Confirmation

John Bollinger coined the term "Head-Fake" to describe a pattern where price initially pierces one band during a squeeze, triggers retail breakout orders, and then violently reverses in the opposite direction.

To avoid false breakout traps:

Wait for the Candle Close: Never enter on an intraday wick poking outside the band; require a full candle body close outside the upper or lower band.
Check Volume Expansion: Authentic breakouts require institutional volume expansion at least 1.5x to 2x the 20-day average. Explore our framework on breakout trading strategies.
Pair with Volatility Tools: Combine Bollinger Bands with Average True Range (ATR) to calibrate stop loss distances and position sizing.

Frequently Asked Questions: Bollinger Bands

What are Bollinger Bands in technical analysis?

Bollinger Bands are a volatility band overlay created by John Bollinger. They consist of three lines: a middle band (typically a 20-period Simple Moving Average) and two outer bands plotted two standard deviations above and below the middle band, dynamically expanding and contracting with market volatility.

What is a Bollinger Band squeeze?

A Bollinger Band squeeze occurs when the upper and lower bands converge to multi-period narrow extremes, reflecting minimal price volatility. Squeezes represent periods of market consolidation that frequently precede sharp, directional volatility expansions.

Does a Bollinger Band squeeze tell you which direction price will break?

No. The squeeze only indicates that volatility has contracted to historically low levels; it does not predict whether the subsequent expansion will break upward or downward. Traders must wait for candle closes outside the band and volume confirmation.

What does 'walking the bands' mean?

'Walking the bands' describes a strong trending condition where price tags or rides along the upper band (in an uptrend) or lower band (in a downtrend) for multiple successive sessions without mean-reverting, signaling strong institutional momentum.

How is BandWidth calculated?

BandWidth is calculated as: (Upper Band - Lower Band) / Middle Band. It normalizes the width between the bands into an objective mathematical metric, enabling algorithmic screening for volatility compression.