Bollinger Bands

Quick Answer

Bollinger Bands are a technical-analysis indicator consisting of a moving average and two bands plotted above and below it using standard deviation. Because standard deviation changes with price volatility, the bands typically widen when volatility increases and contract when markets become quieter. They provide relative price and volatility context rather than guaranteed trading signals.

How do Bollinger Bands work?

Bollinger Bands contain three main lines:

Middle Band = Moving Average

Upper Band = Moving Average + (Standard Deviation × Multiplier)

Lower Band = Moving Average − (Standard Deviation × Multiplier)

A commonly used configuration is a 20-period simple moving average with the upper and lower bands placed two standard deviations away. These parameters can be changed depending on the analysis.

Because standard deviation measures dispersion in price data, the distance between the upper and lower bands changes over time.

When volatility increases:

Bands generally widen

When volatility decreases:

Bands generally contract

This makes Bollinger Bands responsive to changing market conditions rather than keeping the bands at a fixed percentage distance from the moving average.

Key features of Bollinger Bands

Several characteristics are important when interpreting the indicator:

• Three-line structure: Bollinger Bands consist of a central moving average plus an upper and lower band.

• Volatility-sensitive width: The bands expand and contract according to standard deviation.

• Relative price context: Price near the upper band is relatively high compared with the recent range, while price near the lower band is relatively low.

• Customisable parameters: The moving-average period and standard-deviation multiplier can be adjusted.

• Bollinger Band squeeze: Very narrow bands indicate relatively low recent volatility and are often referred to as a squeeze.

• Not inherently directional: Narrowing bands do not identify whether a subsequent price move will be upward or downward. Fidelity specifically notes that a sharp move following tighter bands may occur in either direction.

Simple Bollinger Bands example

Suppose the 20-period simple moving average of an instrument is:

$100

and its 20-period standard deviation is:

$3

Using a two-standard-deviation setting:

Upper Band = $100 + (2 × $3)

Upper Band = $106

The lower band is:

Lower Band = $100 − (2 × $3)

Lower Band = $94

The Bollinger Bands would therefore be approximately:

Upper Band: $106
Middle Band: $100
Lower Band: $94

If volatility later increases and standard deviation rises to $5, while the moving average remains $100:

Upper Band = $110
Lower Band = $90

The bands have widened because recent volatility increased.

This example is illustrative only and does not represent actual FxGrow prices, trading conditions or a recommended indicator setting.

Potential benefits and uses

Bollinger Bands can help provide context about an instrument's recent volatility and relative price position.

They may be used to:

• identify periods of relatively high or low volatility;

• observe volatility expansion and contraction;

• determine whether price is relatively high or low compared with its recent distribution;

• study potential consolidation periods;

• provide context alongside other technical indicators;

• observe periods when price remains close to an upper or lower band during a strong trend.

Fidelity notes that Bollinger Bands are intended to be considered together with other analysis rather than used as standalone confirmation of a trading decision.

Risks, limitations and common misconceptions

A common misconception is that touching the upper Bollinger Band automatically means sell, while touching the lower band automatically means buy.

It does not.

During strong trends, price can remain near or move beyond one band for an extended period. A touch of a band therefore does not guarantee an immediate reversal.

Another misconception is that a Bollinger Band squeeze predicts market direction. Narrow bands indicate lower recent volatility, but they do not establish whether the next significant move will be higher or lower.

Bollinger Bands are also based on historical prices. Moving averages and standard deviations react to data that has already occurred, so the indicator cannot reliably predict future prices.

Finally, the common 20-period, two-standard-deviation configuration is a conventional setting rather than a rule that is automatically suitable for every market, timeframe or strategy.