What it is

Bollinger Bands were developed by John Bollinger in the early 1980s and have become one of the most recognisable overlays in technical analysis. The indicator consists of three lines drawn directly on the price chart: a middle line, which is a simple moving average of price, and two outer bands placed a number of standard deviations above and below that average. Because standard deviation is a direct measure of how dispersed price has been recently, those outer bands literally bend with the market, they widen when the market is volatile and narrow when it goes quiet.

That self-adjusting behaviour is what sets Bollinger Bands apart from fixed envelopes or static support and resistance lines. They give you a moving picture of "normal" price behaviour: most of the time, in any reasonable sample, price will trade inside the two outer bands. When it pushes outside, that is the market telling you something unusual is happening, and that observation is the entry point to almost every Bollinger-based read.

How it works

The middle line is the trend reference, it tells you, on the timeframe you are watching, whether price is broadly above or below its recent average. The outer bands are the volatility envelope. When recent candles have been small and quiet, the standard deviation collapses and the bands squeeze together. When the market starts swinging, the standard deviation expands and the bands fan apart. The visual is intuitive: a tight "squeeze" looks like a pinched neck on the chart and a volatile market looks like a balloon.

The combination of these three lines lets you read two unrelated dimensions of the market at the same time. The slope and position of the middle line tell you about trend; the width of the bands tells you about volatility. Many traders look at the bands first to gauge the climate, and only then turn to price action and other indicators to make a decision. The standard settings, a 20-period average with bands set two standard deviations out, are a sensible starting point on almost any chart.

How to read it

There are three classic Bollinger Band reads.

The first is the squeeze: when the bands narrow to an unusually tight range, the market is coiling and a directional move, in either direction, often follows. The squeeze itself is not a signal; it is a heads-up that something is building. Confirmation comes from the breakout candle, ideally on rising volume, and from the direction of the next few closes relative to the middle line.

The second is the band touch. In a healthy uptrend price will repeatedly tag the upper band and pull back toward, but not through, the middle line; in a healthy downtrend the mirror image happens with the lower band. Treat upper-band touches in an uptrend as continuation, not exhaustion.

The third is the band walk: in very strong trends, price hugs and rides one of the outer bands for many bars in a row. That is one of the cleanest visual signs of a market under one-sided control, and it should make you sceptical of betting against it.

Mean reversion versus breakout

The single most important interpretive question is which mode the market is in. In a range-bound, low-volatility market, mean reversion rules: a tag of the lower band tends to snap back toward the middle, and a tag of the upper band tends to fade. In a trending market the same touches mean continuation, not reversal. Reading the bands without first deciding "are we ranging or trending?" is the fastest way to fight the tape. Use the slope of the middle line and the band width together: flat middle line plus narrow bands favours mean reversion; expanding bands plus a sloping middle line favours breakout follow-through.

Strengths & limits

The strength of Bollinger Bands is that they answer questions you actually have on every chart, "is this big or small?" and "is this a quiet day or a wild one?", and they answer them in the same units as price itself, with no extra panel needed. They work on every timeframe from one-minute scalping charts to monthly investing charts, and the squeeze in particular is one of the few visual setups that translates cleanly across markets and asset classes.

The most common mistake is assuming the outer bands are automatic buy or sell signals. They are not. A touch of the upper band in a strong uptrend is normal and bullish, not a short signal; a touch of the lower band in a panic crash is normal and bearish, not a buy signal. Bollinger Bands describe context; they do not, on their own, pick direction. Pair them with at least one trend tool (a longer moving average or MACD) and one momentum or exhaustion tool (RSI is the classic partner) before you act.

Key takeaway: Bollinger Bands wrap a moving average in standard-deviation envelopes that widen and narrow with volatility; read the squeeze, the band touch, and the band walk for context, but confirm direction with a trend and momentum tool before acting.