Understanding Price Expansion and Contraction
Bollinger Bands measure volatility, trend strength, and potential breakouts. John Bollinger created them in the 1980s. They adapt to market conditions and work for both trend trading and mean reversion.
The three lines are the upper band, the middle band (20 SMA), and the lower band. Standard settings are a 20-period SMA and 2 standard deviations.
Contraction vs Expansion
A squeeze is when the bands narrow. That signals low volatility, indecision, and a higher risk of fakeouts. Most traders wait for expansion instead of trading the chop.
Expansion is when the bands widen. That signals increasing volatility, a new trend, and a higher-probability momentum move. The best opportunities often follow a tight squeeze.
How to Use Bollinger Bands
Mean reversion: a tag of the upper band often returns toward the middle band, and a tag of the lower band often does the same.
Trend filter: price above the middle band is an uptrend; price below it is a downtrend.
Breakouts from compression form after tight bands, a flat mid-band, and quiet volume. Once expansion begins, price often trends for an extended move.
The outer bands can be profit targets or reversal zones. Pair them with MACD, RSI, or stochastics to refine entries.
Alternate Settings
In high volatility, some traders widen the standard deviation to 2.618 so the bands can expand with larger swings. In tight ranges, a shorter period or a negative offset creates tighter bands and faster signals.
Key Takeaways
- Bollinger Bands measure volatility through expansion and contraction
- Contraction is chop; expansion is trend
- The middle band acts as a trend guide
- Upper and lower bands act as reversal or target zones
- They work best with momentum indicators
- Breakouts after compression generate major moves
Pro Tips
- The tighter the squeeze, the bigger the breakout that often follows.
- Price above the 20 SMA middle band is a bullish trend filter.
- Tagging an outer band alone is not a reversal — wait for confirmation.
- Expansion plus consecutive closes outside the band often signals a strong trend wave.
- Combine squeezes with EMAs or MACD for earlier breakout entries.
- Avoid band trading during low-volume chop.