Bollinger Bands Explained
A beginner-friendly explanation of Bollinger Bands: how the bands are calculated from a moving average and volatility, and what traders use them for.
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Bollinger Bands are a volatility-based indicator that wraps a band around price, widening and narrowing as the market gets more or less volatile. They’re easy to spot on a chart once you know what you’re looking at: a moving average line with two bands drawn above and below it.
How Bollinger Bands are built
There are three components:
- Middle band: a simple moving average of price, commonly over 20 periods.
- Upper band: the middle band plus a multiple of the standard deviation of price over the same period, commonly two standard deviations.
- Lower band: the middle band minus that same multiple of the standard deviation.
Standard deviation is simply a statistical measure of how spread out recent prices have been from their average. When price has been moving a lot (higher volatility), the standard deviation grows, and the bands spread further apart. When price has been calm (lower volatility), the standard deviation shrinks, and the bands pull in closer together. The default settings of a 20-period average and two standard deviations are common defaults on most charting platforms, though both numbers can be adjusted to suit a different pair or timeframe.
What the bands are commonly used for
Reading relative volatility
The most direct use of Bollinger Bands is simply as a visual read on whether a pair is currently more or less volatile than its recent history. Wide bands mean recent price swings have been large; narrow bands mean they’ve been small.
“The squeeze”
A period where the bands pull in very tight is sometimes called a squeeze, and some traders watch for it as a sign that volatility has compressed and could expand again in either direction. A squeeze describes low recent volatility — it does not indicate which direction price will move once volatility picks back up, and a squeeze can also persist for a long stretch before anything changes.
Price touching or exceeding a band
Price touching or briefly moving outside the upper or lower band is sometimes read as a sign that a move has become stretched relative to its recent average. This is not the same as a reversal signal: in a strong trend, price can ride along or outside one of the bands for an extended period while continuing in the same direction, since the bands are measuring volatility relative to a short recent average, not a fixed ceiling or floor.
Important honesty about what Bollinger Bands can’t do
Because the bands are built from a moving average and a statistical measure of recent price spread, they are entirely backward-looking — they describe the volatility and average price of the recent past, not a forecast of where price is headed. A touch of the upper or lower band does not confirm that price will reverse, bounce, or continue; all three outcomes are possible, and which one happens depends on far more than what the bands themselves show. The same applies to a squeeze: it flags that volatility has been unusually low, not what will trigger the next expansion or which direction it will favor.
Using Bollinger Bands alongside other analysis
Most traders who use Bollinger Bands treat them as one layer of context — a quick visual sense of current volatility relative to recent history — combined with trend reading, support and resistance, and other tools, rather than as a self-contained trading system. As with every indicator covered in this cluster, no specific pattern involving the bands has a known, fixed rate of leading to any particular outcome, which is exactly why risk management stays essential regardless of what the bands appear to be showing.