Bollinger Bands were developed by John Bollinger in the 1980s and introduced one key insight that most technical tools lack: volatility is dynamic, not constant. Unlike fixed support and resistance levels or momentum oscillators, Bollinger Bands expand when volatility increases and contract when it decreases — creating a self-adjusting envelope around price that reflects current market conditions rather than historical averages. This adaptive quality makes Bollinger Bands genuinely useful across different market environments — but only when you understand which signal applies to which environment.
How Bollinger Bands Are Built
Bollinger Bands consist of three lines. The middle band is a 20-period Simple Moving Average. The upper band is the middle band plus two standard deviations of price. The lower band is the middle band minus two standard deviations. Standard deviation measures how far recent closes have dispersed from the average — when price is moving sharply, standard deviation is high and bands are wide. When price is calm and directionless, standard deviation is low and bands are narrow.
Middle Band: 20-period SMA = 1.0850 Upper Band: Middle + 2 StdDev = 1.0950 Lower Band: Middle − 2 StdDev = 1.0750 Statistically, approximately 95% of price closes should fall within the upper and lower bands — the bands contain the vast majority of recent price action. When price breaches a band, it is a statistically unusual event that warrants attention.
The Squeeze
The squeeze is the most important Bollinger Band signal. It occurs when the bands narrow to an unusually tight range — typically after an extended period of low volatility. Tight bands indicate compressed market energy. Markets tend to alternate between periods of low volatility and high volatility. A squeeze typically precedes a significant directional expansion — a sharp move out of the tight range in one direction.
The squeeze does not tell you which direction the breakout will occur — that is its limitation. Traders who use the squeeze typically wait for the first candle to close convincingly outside the bands after a squeeze period, then enter in that direction. Confirmation from price structure — a breakout from a consolidation pattern — significantly improves the signal quality.
The squeeze sets up the trade. The direction of the first decisive move after the squeeze determines which way you trade it. Do not anticipate the direction — wait for the market to show you.
Walking the Bands
In a strong trend, price can walk along the upper or lower band for extended periods — consistently closing at or near the outer band without reverting to the middle. This band walk is a sign of strong momentum and should be respected — it is not a reversal signal.
Many traders see price touching the upper band and immediately think it is overbought — they sell into a strong uptrend and get stopped out repeatedly. The upper band touch in a trending market confirms momentum, it does not predict reversal. Mean reversion signals from Bollinger Bands are only reliable in ranging markets.
Mean Reversion
In a ranging or sideways market, price touching the outer bands tends to revert to the middle band. This is the mean reversion use of Bollinger Bands — when price touches the lower band in a range and a candlestick reversal pattern forms, the target is the middle band (20 SMA). When price touches the upper band in a range with a bearish signal, the target is the middle band.
Market: EUR/USD ranging between 1.0800 and 1.0950 for 6 weeks. Price touches lower Bollinger Band at 1.0800. A bullish pin bar forms at the band. Entry: Buy above pin bar high. Stop: Below pin bar low. Target: Middle band (20 SMA) at 1.0875. Risk-Reward: approximately 1:2. This setup works in ranging markets. In trending markets, the same setup would likely fail — price touching the lower band in a downtrend is confirming the trend, not reversing it.
Bollinger Band Width
Bollinger Band Width is a derived indicator that measures the distance between the upper and lower bands relative to the middle band. It provides a cleaner way to identify squeezes — Band Width at multi-month lows indicates an unusually tight squeeze and an impending volatility expansion. Some traders use Band Width as their primary squeeze identification tool rather than visually estimating the band compression.