TL;DR
Bollinger Bands plot a 20-period moving average with an upper and lower band two standard deviations away. The bands widen when volatility rises and squeeze when it falls. A squeeze hints a breakout is coming; %B tells you where price sits inside the bands; touching a band alone is not a reversal signal.
What Are Bollinger Bands?
Bollinger Bands, created by John Bollinger, wrap price in a three-line envelope. The middle band is a simple moving average (default 20). The upper and lower bands sit a set number of standard deviations (default 2) above and below it. Because standard deviation is a direct measure of volatility, the bands breathe: they expand when price gets volatile and contract when the market goes quiet. Statistically, roughly 95% of price action stays inside 2-standard-deviation bands, which is what makes excursions outside them meaningful.
Traders read the bands several ways:
- The squeeze: when the bands contract to an unusually narrow width, volatility is compressed and a breakout is often near. The squeeze is the most-watched Bollinger setup.
- Band walks: in a strong trend, price hugs the upper band (uptrend) or lower band (downtrend) for many bars. This is continuation, not reversal.
- Mean reversion: in a range, price tends to oscillate from one band back toward the middle MA, giving fade entries.
- %B and bandwidth: %B normalises where price sits inside the bands (0 = lower, 1 = upper); bandwidth quantifies how wide the bands are, making squeezes measurable.
The core mistake traders make is treating Bollinger Bands as a pure reversal tool — assuming an upper-band touch means “sell.” In trends, that’s a recipe for fighting the move. The bands describe volatility and relative position, not direction; direction has to come from context.
Key Formula / Numbers
Middle Band = SMA(20)
Upper Band = SMA(20) + (2 × standard deviation of price over 20)
Lower Band = SMA(20) − (2 × standard deviation of price over 20)
%B = (Price − Lower Band) / (Upper Band − Lower Band)
Bandwidth = (Upper Band − Lower Band) / Middle BandCommon settings:
| Setting | Default | Tighter | Wider |
|---|---|---|---|
| Period | 20 | 10 | 50 |
| Std Dev | 2.0 | 1.5 | 2.5 |
How Quantzee Uses This
Quantzee’s Bollinger Bands Pro+ upgrades the classic bands into a full volatility toolkit. It detects squeezes using a Keltner-channel overlap with a duration counter, so you see not just that volatility is compressed but how long the squeeze has lasted — longer squeezes tend to resolve more violently. On the break it reads a momentum-based breakout-direction bias to lean the trade the right way, and a Trend/Reversion classifier tells you whether the current regime favours riding band walks or fading toward the middle band. A %B divergence engine flags when price makes a new extreme but its band position doesn’t, and a multi-timeframe squeeze dashboard confirms whether higher timeframes are coiled too. All signals are non-repainting, locked at bar close.
How to Identify a Bollinger Band Squeeze
A squeeze occurs when bandwidth — the distance between the upper and lower bands relative to the middle band — reaches a multi-month low. Several methods exist to identify squeezes objectively:
- Keltner Channel overlap method: when the Bollinger Bands (2 std dev) contract inside the Keltner Channels (1.5 × ATR), the market is in a statistically significant low-volatility state. This is the most commonly used mechanical squeeze definition, popularised by John Carter and used in Quantzee’s Bollinger Bands Pro+.
- Bandwidth percentile method: measure current bandwidth against the rolling minimum/maximum bandwidth over a lookback period. Bandwidth below the 10th–20th percentile indicates a squeeze.
- Visual method: the bands appear nearly parallel and unusually narrow relative to recent history.
The duration of the squeeze matters. A one-bar squeeze may be noise; a squeeze sustained for 10+ bars indicates genuine volatility compression and tends to resolve in a sharper move. Quantzee’s BB Pro+ includes a squeeze duration counter for this reason — it shows how many bars the current squeeze has lasted.
Bollinger Bands in Different Market Regimes
Bollinger Bands behave differently in trending versus ranging markets, and reading the regime first changes how you use them:
In a range (choppy, sideways):
- Mean reversion works: price oscillates between upper and lower bands
- Enter near the lower band when RSI is oversold; take profit near the middle band or upper band
- %B below 0.1 (price near lower band) = potential long; %B above 0.9 = potential short
- Avoid breakout trades — breakouts from inside a range resolve back to the range more often than they follow through
In a trend (strong directional move):
- Band walks dominate: in a strong uptrend, price closes above or near the upper band on multiple consecutive bars
- Do NOT fade upper-band closes in a trend — that is the signal of trend strength, not reversal
- The middle band (20-SMA) becomes the key support/resistance: pullbacks to it in a trend are buy opportunities (uptrend) or sell opportunities (downtrend)
- %B staying above 0.5 throughout a trend indicates persistent bullish strength
Bollinger Band Width as a Volatility Measure
Bandwidth is an underused Bollinger tool. It quantifies the current width of the bands as a percentage of the middle band:
Bandwidth = (Upper Band − Lower Band) / Middle Band × 100Rising bandwidth = expanding volatility (breakouts, trending moves). Falling bandwidth = contracting volatility (squeezes, ranges). Tracking bandwidth over time lets you objectively measure whether today’s bands are wider or narrower than historical norms — the numerical backbone of squeeze detection.
Common Mistakes
- Selling every upper-band touch: in an uptrend price walks the upper band. Fading band touches without a regime check means repeatedly shorting strength. Confirm whether you’re trending or ranging first.
- Trading the squeeze direction blind: a squeeze tells you a move is coming, not which way. Wait for the actual break (and ideally a momentum or volume confirmation) instead of guessing direction inside the squeeze.
- Ignoring the middle band: the 20-period MA is the anchor — in trends it often acts as dynamic support/resistance. Traders who only watch the outer bands miss the most useful line on the chart.
- Treating all band touches equally: a band touch after 20 bars of trend-walking is different from a first-touch reversal. Context — how long price has been near the band, whether RSI is diverging, whether volume is expanding — determines the quality of the signal.
Frequently Asked Questions
Are Bollinger Bands good for crypto trading?
Yes. Bollinger Bands are widely used in crypto markets because crypto assets are highly volatile and exhibit strong squeeze-breakout patterns. Bitcoin, Ethereum, and major altcoins frequently display multi-day or multi-week periods of low volatility (tight bands) followed by sharp directional moves. The squeeze setup and %B readings are particularly useful in 1H and 4H crypto charts. The same 20-period, 2-standard-deviation default applies, though some crypto traders use 20/2.5 to account for the higher baseline volatility.
What does it mean when price is outside the Bollinger Bands?
When price closes outside the upper band, it means price has moved more than 2 standard deviations above the 20-period average — statistically unusual but not an automatic sell signal. In trending markets, band excursions are common and can persist for multiple bars. In a range, a close outside the band followed by a close back inside it is a reversal signal (the band-walk failed). Context is everything — check whether the broader trend is up or down before interpreting an excursion as extreme.