FX Bollinger Bands Guide — Squeeze and Expansion

Bollinger Bands are a volatility-aware moving average overlay used to gauge whether price is stretched relative to its recent range. In practice, they work best as a context tool — telling you what kind of market you’re in — rather than a standalone signal.

How the bands are constructed

Standard settings use a 20-period simple moving average (SMA) plus and minus two standard deviations (2σ) of the same series. That means:

• The middle line is the 20-period mean.
• The outer bands expand and contract with volatility.
• Roughly 95% of price action statistically falls inside the bands.

Reading the three primary states

By contrast with simpler indicators, the bands change shape based on what the market is doing.

• Squeeze — bands narrow as volatility falls. This is often used when traders prepare for a breakout, though direction isn’t given by the squeeze itself.
• Expansion — bands widen during trending moves. The prevailing direction tends to persist while expansion holds.
• Band walk — price hugs the outer band repeatedly. Strong trends ride the upper or lower band, and counter-trend trades against a band walk frequently get stopped out.

Practical use cases

In short, Bollinger Bands are most useful for two questions:

1. Is volatility expanding or contracting right now?
2. Is price stretched relative to its 20-period mean?

Combine the bands with a separate trend filter (such as a 200 EMA) or a momentum indicator before acting on extremes. Touching the outer band alone is not a reversal signal.

Risks to flag

Bollinger Bands lag price by definition — they’re built from a moving average. They will not catch turning points perfectly, and in low-volatility ranges the bands themselves can give false breakout signals. Risk-size every trade independently of indicator readings.

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