Bollinger Bands Trading Guide: Squeezes, Breakouts and Mean Reversion

The standard version uses a moving average as the middle band and places upper and lower bands a chosen number of standard deviations away. A common default is a 20-period moving average with bands two standard deviations above and below it.

Because standard deviation changes with recent price movement, the envelope automatically expands when volatility rises and contracts when volatility falls.

A squeeze occurs when the bands become unusually narrow, signalling volatility compression. Markets often cycle between contraction and expansion, so traders watch squeezes for the possibility of a larger move developing.

The squeeze does not identify direction. A complete strategy needs a directional trigger such as a close outside a range, a trend filter, momentum confirmation, or a break of market structure.

One breakout approach waits for price to close outside a band after a period of compression. Another requires the band width itself to start expanding, indicating that volatility is returning.

Strong breakouts can continue along the outer band rather than immediately reversing. Traders therefore need to distinguish continuation logic from mean-reversion logic before entering.

Mean-reversion strategies may look for price to stretch to an outer band and then show evidence of rejection back toward the middle band. The setup is usually stronger when the broader market is balanced rather than strongly trending.

A band touch alone is not enough. In a persistent trend, repeated attempts to fade the outer band can create a sequence of losses. Regime filters and hard invalidation points are important.

The middle moving average can act as a dynamic reference for trend and value. Price holding above it with an upward slope can support a bullish context, while repeated failure below a falling middle band can support a bearish context.

As with any moving average, the signal lags price and can become noisy in sideways conditions. It should be treated as one component of the setup.

Band width can be measured directly and compared with its historical range. This gives traders an objective way to identify unusually compressed or expanded volatility rather than relying on visual judgement.

A filter might require band width to be below a percentile before a squeeze trade or above a threshold before a trend trade. The threshold should be validated out of sample.

The most common mistake is assuming upper band equals overbought and lower band equals oversold. In a strong trend, price may remain near an outer band for many bars because the trend itself is driving the extension.

Another mistake is mixing breakout and reversal rules without deciding which market regime is being traded. A strategy should clearly define when it expects continuation and when it expects reversion.

Document the moving-average length, deviation multiplier, entry trigger, trend filter, stop, target, and whether orders use intrabar touches or confirmed closes. These choices can produce very different results.

Test nearby parameters and separate trending from range-bound periods. A robust strategy should retain acceptable behaviour when the settings or cost assumptions are changed modestly.