Level 2 · Lesson 6 / 11 · English
Bollinger Bands
4 min reading · Exercises take additional time
0 of 11 lessons completed for this visit
Bollinger Bands surround a moving average with envelopes based on recent price dispersion. They describe price location and changing variability, not guaranteed turning points. The related chart contains computed hypothetical observations; band touches and contractions are teaching examples rather than predictions about any real instrument.
What you will learn
- Calculate bands from a mean, standard deviation and multiplier.
- Distinguish dispersion from a forecast probability.
- Evaluate band touches, squeezes and implementation settings.
Illustrative educational chart · Not live market data
The middle line and envelopes
A common configuration uses a 20-period SMA of closes as the middle band and a multiplier of two. Upper band = mean + multiplier × standard deviation. Lower band = mean − multiplier × standard deviation. The standard deviation describes dispersion of the selected prices around their mean within the lookback window.
Implementations may use population standard deviation, dividing squared deviations by n, or sample standard deviation, dividing by n − 1. These produce different band widths. Record the convention, period, price input and multiplier when reproducing results. The standard deviation of price levels is also not the same statistic as the standard deviation of returns.
Touches and band walking
A close near the upper band is high relative to the rolling mean and dispersion. That observation does not establish overvaluation or require an immediate short position. In a strong trend, price may repeatedly approach or exceed the same band, sometimes called walking the band. Automatic fading can therefore create repeated losses.
In a range, a return toward the mean may be a hypothesis worth testing, but it needs precise rules. Specify whether a touch uses the high, close or executable bid/ask. The developing band itself changes as new prices arrive. A historical chart should not be read as though every final band position was known throughout the candle.
Squeezes, expansion and uncertainty
Narrowing bands show lower recent dispersion under the chosen settings. A squeeze may precede greater movement, but it does not specify the direction, start time or size of that movement. Narrow bands can persist, and an initial breakout can fail. Wider bands indicate increased measured dispersion, not automatically a better trading opportunity.
Do not assume that two-standard-deviation bands contain a fixed percentage of future prices. Familiar normal-distribution coverage statements require assumptions that rolling financial prices generally do not satisfy. Test any breakout or mean-reversion idea across different regimes, include costs and define independent exposure limits. Band width is not a guarantee that losses stay within the envelope.
Key terms
- Middle band
- The moving average around which the envelopes are drawn.
- Standard deviation
- A measure of dispersion around a specified mean.
- Squeeze
- A descriptive term for relatively narrow bands.
Hypothetical worked example · Not live market prices
Hypothetical bands around a mean of 100
- Assume the rolling mean is 100 and the chosen standard deviation is 2.
- With multiplier 2, the offset is 2 × 2 = 4.
- Lower band = 100 − 4 = 96; upper band = 100 + 4 = 104.
| Band | Calculation | Value |
|---|---|---|
| Lower | 100 − 2 × 2 | 96 |
| Middle | Mean | 100 |
| Upper | 100 + 2 × 2 | 104 |
Simplified educational calculations. Costs, slippage and provider-specific adjustments apply where relevant; these are not actual returns.
Common mistakes to avoid
- Treating every upper-band touch as a sell command.
- Assigning a fixed future coverage probability to the bands.
- Comparing bands without checking the standard-deviation convention.
Lesson summary
Bollinger Bands describe rolling price location and dispersion. A touch, squeeze or expansion requires context and testing rather than a fixed predictive interpretation.
Practical exercise
Keep mean 100 and multiplier 2, but increase standard deviation to 3. The bands become 94 and 106. Explain why this widening alone does not reveal the next direction.
Knowledge check
Check your understanding
Results apply to this attempt only and are not saved to a student account. No certificate is issued.
Answer all questions correctly and complete the exercise. Progress follows you between Academy pages for this visit only; it is not saved to an account and resets on reload.
Related lessons
Financial education, not personal investment advice. Leveraged Forex and CFDs can lead to substantial losses. Demo practice and correct quiz answers do not guarantee trading success.