Technical analysis · Intermediate

Bollinger Bands

Bollinger Bands measure volatility, not value. A touch says this candle is unusual against the last twenty, and nothing more than that.

Last reviewed 15 September 2026 by the MarketPro research desk · Editorial policy

In short

Bollinger Bands plot a moving average, usually 20 periods, with two lines set a number of standard deviations above and below it, normally two. The bands widen when volatility rises and narrow when it falls. A touch of a band means the current price is unusual relative to the recent window, not that it is too high or too low. In a strong trend price can close outside the band repeatedly while the whole envelope drifts with it.

What to remember

A band touch is not a reversal signal. In a trend price walks the band, closing outside it repeatedly while the envelope drifts along.
A squeeze tells you volatility is compressed and often precedes expansion. It says nothing about direction, so prepare both sides.
Mean reversion logic only applies when the middle band is flat. A sloping middle band means the mean itself is moving.
The bands lag their own inputs. The envelope is widest just after the move you wanted it to warn you about.

Lesson 11 of 26 in Technical analysis

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Bollinger Bands are a volatility envelope, not a boundary

Bollinger Bands plot a moving average with two lines above and below it, spaced by a multiple of the standard deviation of price. The standard setup is a 20-period simple moving average with bands two standard deviations away. Because standard deviation measures dispersion, the bands widen when price becomes turbulent and narrow when it settles. The envelope is measuring volatility, and it is doing nothing else.

The most common misreading follows directly from the maths. Two standard deviations contains roughly 95% of observations in a normal distribution, which is where the idea comes from that touching a band is extreme. Price is not normally distributed, the standard deviation is calculated from the same recent window that produced the touch, and a strong trend simply drags the whole envelope along with it. A band touch is not a boundary. It is the statement that this candle is unusual relative to the last twenty.

The squeeze

When the bands contract, recent price movement has been small and uniform. Volatility tends to cycle between quiet and active, so a long period of contraction often precedes a period of expansion. That is the useful observation behind the squeeze, and it is genuinely one of the more durable ideas in indicator-based analysis.

What the squeeze does not do is tell you which way. A squeeze that resolves upward and one that resolves downward look identical beforehand. Anyone presenting a squeeze as a directional setup has added a directional view from somewhere else and attributed it to the bands. The honest use is preparation: mark both boundaries, decide what you would do in either direction, and size the trade for the volatility you expect after expansion rather than the volatility you see during the quiet.

Walking the band

In a strong trend, price does not touch the upper band and reverse. It rides it, printing candle after candle with the close near or beyond the upper line while the whole envelope drifts higher. This is called walking the band, and misreading it costs more than any other mistake made with this indicator.

Consider a pair rallying from 1.0900 to 1.1150 over three weeks. Price closes above the upper band eleven times in that run. A trader treating each touch as a sell signal has taken eleven trades against a 250 pip trend. Even at a modest 30 pips of risk each, that is a large number in cash and a much larger number in confidence. Running one of those losses through the pip calculator in your own account currency is a fast way to make the lesson stick.

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When mean reversion actually applies

Defined range. Price oscillating between two horizontal levels with a flat middle band is the condition where a move to a band has a reasonable chance of returning to the average.
Flat middle band. The 20 SMA sloping sideways is the clearest sign that mean reversion logic is live. A sloping middle band means there is a trend, and the mean is moving.
Confirmation, not the touch. Waiting for a close back inside the band after a touch outside removes a whole class of entries taken into a move that was not finished.
Target the middle, not the far band. In a range, the average is the honest objective. Expecting a full traverse to the opposite band is asking for the whole range in one go.

The limits of the envelope

The bands lag their own inputs. A volatility spike widens the bands after the spike, so the envelope is always widest just after the move you wanted it to anticipate.
The setting is a convention. 20 and 2 are defaults, not laws. Narrower bands produce constant touches, wider ones almost none, so any rule about touching is a rule about your settings.
They give you no invalidation. A band is a moving line, which makes it a poor place to put a stop. The stop still has to come from structure or a volatility multiple.
Squeezes can fail. A contraction can resolve into a small break that immediately returns inside the range, then contract again. Low volatility is not a promise of a big move, only a tendency.

Classify the day before you trade it

Use the bands as a regime classifier rather than a trigger. Each morning, on your main timeframe, write down one of three states: squeezing, expanding, or walking. Squeezing means prepare both directions and wait. Expanding means widen stops and reduce size, because the same structural stop now needs more room. Walking means the trend tools apply and the mean reversion rules are switched off.

That single classification changes what you allow yourself to do for the day, and it is far more useful than any signal the bands can produce on their own. Because expanding volatility changes stop distance, it changes position size too, so recheck the number in the position size calculator rather than carrying yesterday's lot size into a different market. The broader idea of matching size to conditions is covered in the risk management guide.

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Written and reviewed by the MarketPro research desk

MarketPro is a trading-signal and trading-education app operated by Harajuku Holdings LTD (Cyprus). Our signal desk publishes and tracks every trade idea in-app, and every page here is checked against the app's live behaviour before publishing. Last reviewed 15 September 2026. How we produce signals and content · About MarketPro

FAQ

Bollinger Bands: questions

What does a Bollinger Band squeeze mean?

A squeeze is a period where the bands contract because recent price movement has been small and uniform. Volatility tends to alternate between quiet and active phases, so a prolonged squeeze often precedes a larger move. The squeeze gives no directional information, so the practical use is marking both boundaries and preparing for either resolution.

Should you sell when price touches the upper Bollinger Band?

Not on the touch alone. A close above the upper band means the candle is unusual relative to the last twenty, which is exactly what a strong trend produces. In a sustained move price can close outside the band many times in a row. Mean reversion logic only carries weight when the middle band is flat and the market is clearly ranging.

What are the best Bollinger Band settings?

The 20-period average with two standard deviations is the standard, and it is a convention rather than an optimum. Tightening to 1.5 deviations produces frequent touches and widening to 2.5 produces almost none, so any rule about band touches is really a rule about your chosen setting. Change it once, for a stated reason, and retest the rule after you do.

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