Most indicators measure momentum or trend. Bollinger Bands measure something different and just as useful: volatility. Developed by John Bollinger, they draw a visual envelope around price that expands when markets get wild and contracts when they go quiet — turning volatility into something you can see at a glance.
The three lines
Bollinger Bands are made of three components plotted on the price chart:
- The middle band — a simple moving average, most commonly the 20-period SMA.
- The upper band — the middle band plus a set number of standard deviations (typically 2).
- The lower band — the middle band minus the same number of standard deviations.
Because the bands are based on standard deviation, they respond directly to volatility. When price swings get larger, the bands widen; when price calms down, they narrow.
What the width tells you
The distance between the bands is the whole point:
- Wide bands mean high volatility — price is moving a lot.
- Narrow bands mean low volatility — the market is quiet and coiled.
Price tends to spend most of its time between the bands, so the bands give you a sense of what's a "normal" range and what's an extreme stretch.
The squeeze
The most watched Bollinger signal is the squeeze — when the bands contract tightly together during a period of low volatility. A squeeze often precedes a strong move: markets rarely stay quiet forever, and a tight squeeze can be the calm before a breakout.
Warning
A squeeze tells you a big move may be coming — but not which direction. Don't assume a breakout will go up just because price is near the upper band. Wait for the actual break.
The classic beginner mistake
Many beginners treat the bands as automatic signals: price touches the upper band, so sell; price touches the lower band, so buy. This is a trap. In a strong trend, price can "ride" the upper band higher for a long time, or hug the lower band down — touching a band is not a reversal signal.
Risk
Touching a Bollinger Band is not a buy or sell button. In a strong trend, price can stay pinned to a band far longer than you expect. Treat the bands as context, not commands.
Using Bollinger Bands sensibly
The bands work best as a volatility gauge alongside other tools:
- Read volatility, not direction — use band width to judge how active the market is.
- Watch for squeezes as a heads-up that a bigger move may be brewing.
- Confirm with trend and price action before trading any band touch or breakout.
- Always use a stop loss, since band-based trades can fail like any other.
See volatility in motion
Bollinger Bands make the most sense when you watch them breathe with the market. A regulated broker with a free demo lets you plot them on live charts and spot squeezes before risking money.
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