Complete Guide to Bollinger Band Squeeze
— How to Detect Before Volatility Explosion
A Bollinger Band Squeeze is a signal that a volatility explosion is imminent as the band width contracts extremely. Just like a spring bounces back stronger the more it is compressed, the narrower the band, the stronger the directional breakout tends to be afterward.
What is a Bollinger Band Squeeze?
Bollinger Band Squeeze refers to a state where the distance between the upper and lower bands of the Bollinger Bands (band width) is abnormally narrow. A narrow band width indicates that the price volatility has drastically decreased over a certain period, meaning that buying and selling forces are balancing out in a narrow price range, accumulating energy.
Market volatility does not contract indefinitely in one direction; it has a tendency to contract → expand → contract repeatedly. Therefore, after a period of extreme contraction, there tends to be a subsequent expansion (breakout) phase where volatility increases again. This is similar to the principle that the deeper a spring is compressed, the stronger the force of its bounce back.
Why Does Volatility Contraction Lead to 'Explosion'?
When trading ranges narrow during a prolonged sideways movement, significant buy and sell orders accumulate in that range. If a meaningful change in supply and demand or news appears at this time, the force trying to break out of the narrow box can digest the accumulated orders all at once, resulting in a large directional movement. While volatility contraction does not guarantee an upward movement, it serves as a preliminary signal indicating "a big movement is about to occur."
How to Calculate Band Width
Bollinger Bands are typically composed as follows:
- Middle Line = 20-day Simple Moving Average (SMA20)
- Upper Line = SMA20 + (2 × 20-day Standard Deviation)
- Lower Line = SMA20 − (2 × 20-day Standard Deviation)
When assessing a squeeze numerically, band width is used.
Band Width = (Upper Line − Lower Line) ÷ Middle Line × 100
By normalizing with the middle line as the denominator, it allows for comparison of the degree of volatility contraction between different stocks, even if they are at different price levels. When the standard deviation decreases, the band width also narrows.
Squeeze Judgment Criteria — 'Percentile' Rather Than 'Absolute Value'
A fixed criterion like "if the band width is below X%" is less meaningful because the volatility characteristics vary by stock. Therefore, it is more accurate to judge where the current value stands in the percentile of the band width distribution over the past year (about 252 trading days).
Practical Interpretation — Squeeze Alone is Not Enough
The decisive limitation of a squeeze is that it does not indicate direction. A volatility explosion can occur upwards or downwards. Therefore, a squeeze should be combined with other indicators that reinforce directionality rather than used alone.
- OBV Accumulation — Whether funds are flowing in during a quiet sideways movement (upward bias)
- Relative Strength (RS) — Whether it is strong compared to the market
- ADX·DI — Whether the trend actually strengthens after a breakout
- RSI — Check entry timing based on overbought/oversold conditions
Utilization in DawnScan
DawnScan scans all US stocks daily and combines the Bollinger Squeeze not as a standalone signal but with OBV accumulation, relative strength, and trend indicators, giving higher scores to stocks where volatility is condensing while an upward bias is observed. How the squeeze is classified as a 'pre-breakout early signal' in conjunction with other signals can be checked in the Overview of Pre-Breakout Early Signals and Methodology, and the stocks actually captured today can be seen in Today's Scan.