Key Takeaways
- Bollinger Bands plot a moving average with an upper and lower band set a number of standard deviations away, automatically widening and narrowing with volatility.
- A "squeeze," where the bands pull tightly together, shows unusually low volatility and often precedes a larger move.
- Price touching or briefly piercing a band is not automatically a reversal signal, in a strong trend price can "walk the band" for an extended stretch.
- Bollinger Bands measure volatility, not direction, so they work best combined with a trend or momentum indicator.
- You can overlay Bollinger Bands on any chart in our free backtesting tool.
What Are Bollinger Bands?
Bollinger Bands, developed by John Bollinger in the 1980s, are a volatility indicator made up of three lines: a middle band, typically a 20-period simple moving average, and an upper and lower band plotted a set number of standard deviations, usually 2, above and below it. Because standard deviation is a direct measure of how spread out recent prices have been, the bands expand automatically when the market gets more volatile and contract when it calms down, without needing any manual adjustment.
This makes Bollinger Bands a volatility tool first and foremost, the third of the three indicator categories introduced in our technical analysis overview, alongside trend tools like moving averages and momentum tools like RSI.
The Squeeze: Reading Low Volatility
When the upper and lower bands pull in close to the middle band, it's called a squeeze, and it reflects a period of unusually low volatility. Markets tend to cycle between calm and volatile phases, so a squeeze is widely watched as a sign that a bigger directional move may be building, even though the bands themselves give no clue which direction that move will break.
Band Touches Are Not Automatic Signals
The most common misreading of Bollinger Bands is treating a touch of the upper band as "overbought, sell" and a touch of the lower band as "oversold, buy." In a genuinely strong trend, price can ride along the upper or lower band for an extended series of candles, a behavior traders call walking the band, without reversing at all. Treating every band touch as a reversal signal in a strong trend produces a string of losing trades against that trend.
A band touch is more useful read in context: in a range-bound, non-trending market, touching the outer bands genuinely does tend to mark the edges of that range. In a trending market, the same touch is often just confirmation the trend is intact and strong.
Combining Bollinger Bands With Other Tools
Because Bollinger Bands describe volatility, not direction, they're most useful paired with a tool that does read direction or momentum:
- With trend: only treat a lower-band touch as a potential buy when the broader trend, judged by a moving average as covered in our moving averages guide, is flat or up, not firmly down.
- With momentum: a band touch alongside RSI showing genuine oversold or overbought conditions, see our RSI guide, carries more weight than the band touch alone.
- With price action: a candlestick reversal pattern (covered in how to read candlestick charts) forming right at a band is a stronger confirmation than the band by itself.
Practice Reading Bollinger Bands on Real Charts
You can add Bollinger Bands (20, 2) directly onto any chart in our free backtesting and market replay tool, across 17 markets and 7 timeframes, and step through real historical squeezes and breakouts bar by bar to see how they actually played out.
Frequently Asked Questions
What does it mean when Bollinger Bands are very narrow?
A narrow band spread, a squeeze, shows volatility is unusually low relative to recent history. It doesn't say which way price will eventually break, only that a volatility expansion, often a sharp one, is statistically more likely to be approaching.
Is touching the upper Bollinger Band a sell signal?
Not on its own. In a strong uptrend, price can repeatedly touch or ride the upper band without reversing. A band touch is more meaningful when combined with a momentum reading or price action signal, rather than traded in isolation.
What settings do most traders use for Bollinger Bands?
The original default, a 20-period moving average with bands set 2 standard deviations away, remains the standard setting used on most charting platforms, including our backtesting tool, and is a sensible starting point before experimenting with other settings.
How are Bollinger Bands different from a regular moving average?
A plain moving average only shows the average price trend. Bollinger Bands add the upper and lower volatility envelope around that same moving average, so you get both the trend line and a read on how wide or narrow current price swings are relative to recent history.