What Bollinger Bands actually measure

Bollinger Bands consist of three lines: a 20-period simple moving average (SMA) in the center, plus an upper and lower band positioned two standard deviations away from that average.

Under normal market conditions, roughly 95% of price action stays inside the bands. When price pushes outside them, it signals that volatility or momentum may be expanding beyond normal expectations.

The two market states that matter most

  • Squeeze — the bands contract tightly together. This reflects low volatility and compressed price action. Markets rarely stay compressed for long, so a directional move often follows.
  • Expansion — the bands widen rapidly after a breakout. This signals volatility expansion and usually confirms that a trend is already underway.

In practice, the longer the squeeze lasts, the more aggressive the eventual move tends to be.

Three high-quality Bollinger setups

  1. Squeeze breakout: the bands remain narrow for an extended period, then price closes outside one band with strong volume. Traders typically enter in the breakout direction and place stops near the opposite band.
  2. Band ride: during strong trends, price can repeatedly “walk” the upper or lower band. This is a sign of trend strength — not necessarily overextension.
  3. Mean reversion at the bands: inside a clear range, touches of the upper band combined with overbought RSI may signal short opportunities, while touches of the lower band combined with oversold RSI may signal longs.

The classic beginner mistake

Many traders assume every touch of the upper band means “overbought.” That interpretation is dangerous in trending markets.

During strong uptrends, the upper band often acts more like dynamic support than resistance. Price hugging the upper band usually signals strength, not weakness.

Before trading mean reversion setups, always identify the broader market regime — especially the higher timeframe trend direction.