Bollinger Bands
Bollinger Bands draw a dynamic channel at "MA ± 2 standard deviations": the band widens and squeezes with volatility, and price spends most of its time inside.
What it is
Bollinger Bands have three lines: a middle band (default SMA20) and upper/lower bands set two standard deviations away. Because standard deviation measures how far price strays from its mean, Bollinger Bands are a volatility-adaptive channel: the band widens when the market gets wild and squeezes when it calms down. The bands answer two questions at once: is volatility currently high or low, and where does price sit relative to its "normal range"?
Origin
Bollinger Bands were created by American analyst John Bollinger in the 1980s. His core insight: volatility is dynamic, so a fixed-width channel (like earlier percentage envelopes) can never fit a market that swings between calm and frenzied — band width must be customized to the current volatility. Bollinger Bands remain the most widely used volatility channel and the name is trademarked.
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The three lines:
StdDev is the standard deviation of the last 20 closes around their mean. Statistically, ±2 standard deviations covers about 95% of a normal distribution — so "price at the band" intuitively means: price is now in the most extreme 5% of the last 20 periods. Fat tails make this an approximation, not a guarantee.
Worked example
Two classic scenarios to build the right intuition:
- Scenario 1: after weeks of range, the band squeezes to its narrowest (the squeeze) — volatility is compressed to a floor and energy is coiling. The eventual directional breakout tends to be explosive (sideways first, then vertical).
- Scenario 2: in a strong trend, price "walks the band" — repeatedly touching the upper band. That is not an overbought short signal; it is the signature of a powerful trend: during volatility expansion price can ride the band for weeks.
The same "touch of the upper band" is a buy signal right after a squeeze-break and a exhaustion warning only late in a long rally — Bollinger signals always depend on which volatility phase the channel is in. Memorizing one rule is not enough.
How to read it
Standard reading of each element:
| Range | Common interpretation |
|---|---|
| Very narrow band (squeeze) | Volatility compressed to a floor — a decision window is near; direction unknown, wait for the break |
| Band expanding | A new volatility cycle is starting, usually with a trend — trade with it |
| Price walking the upper/lower band | Trend is healthy and strong — do not fade it |
| Band touch followed by a fast retreat | In a trend: fading momentum; in a range: the high-probability mean-reversion cue |
| Price ping-ponging inside | Range regime — the bands become boundaries for reversion trades |
The BB dilemma: a band touch means "revert" in ranges but "follow" in trends — judging which regime you are in matters more than memorizing the rules. That is why Bollinger Bands are almost always paired with a trend tool (MA/ADX/MACD).
Common signals & usage
The squeeze breakout
Band width at a multi-week low, then a breakout on volume — the classic prelude of a trend, as volatility goes from compressed to expanding. Direction comes from the break, not from prediction.
Walking the band
In a strong trend, repeated upper-band touches with shallow pullbacks support holding/adding — until price falls back inside the band and the width starts contracting.
Range reversion
In a clear range: buy the lower band, sell the upper, target the middle band — the textbook reversion template, but only with a range-regime premise.
The W-bottom confirmation
Bollinger's own pattern: the second low pierces the lower band then closes back inside (a failed break), while RSI prints a higher low than the first — a materially stronger W-bottom.
Limitations & common mistakes
- "Sell the upper band" is the cardinal mistake: in trends price can walk the band for weeks. A touch says price is at an extreme, not that it will reverse.
- The squeeze has no direction: it tells you a break is coming, not which way — predicting the direction is gambling; trade the confirmed breakout.
- Fat tails break the statistics: the 95% figure assumes a normal distribution, but price distributions have fatter tails — extreme excursions happen more often than the math suggests.
- Parameters vs. market character: 20/2 is the default; high-volatility instruments (crypto) often need 22/2.5 or wider, or you get band touches every day.
- Never use it alone: Bollinger Bands give relative position and volatility, not direction — without a trend read, band signals are a coin flip.
BOLL in MT5
Bollinger Bands are a built-in MT5 trend-type indicator (a three-line channel). The MQL5 function for programmatic use is iBands:
| MQL5 function | iBands() |
| Default parameters | bands_period=20, deviation=2.0 |
| Default applied price | PRICE_CLOSE |
| Buffers | 0=middle (BASE_LINE), 1=upper (UPPER_BAND), 2=lower (LOWER_BAND) |
| Display window | Main chart overlay (channel) |
MT5's deviation parameter is a double (default 2.0), so fractional multipliers like 2.5 work directly. Mind the buffer order when coding: 0 = middle, 1 = upper, 2 = lower.
Behavior across timeframes
15-minute
Popular for intraday reversion, but filter hard — take reversion trades only in the direction of the larger-trend pullback
1-hour / 4-hour
The main field for squeeze-break structures; band width shows the volatility cycle clearly
Daily
The native habitat of the classic 20/2 settings; W-bottom confirmations and band-walking reads are most representative here
Weekly
Weekly squeezes are rare but heavy — a prelude to multi-month decision points
Indicator combinations
Common pairings for Bollinger Bands:
- With RSI: lower-band touch + RSI recovering from oversold is a double-confirmed reversion; upper-band touch + RSI divergence is an exhaustion warning. RSI
- With MA: the BB middle band is an SMA20 — use longer MAs (MA50/200) for direction and the channel only for timing. MA
- With ATR: both measure volatility — ATR places stops, Bollinger structures entries. Complementary, not redundant. ATR
Symbols commonly watched with BOLL
Symbol pages that list this indicator as a common tool:
FAQ
Q What do the ±2 standard deviations mean?
The middle band is a 20-period MA; the outer bands sit two standard deviations either side. By normal-distribution approximation about 95% of prices fall inside — a band touch means price is in the most extreme 5% of the recent window. Fat tails make it an approximation, not a promise.
Q What does a Bollinger squeeze mean?
A narrowing band = volatility compressed to a low; the market is coiling and a decision window approaches. The squeeze gives no direction — that comes from the confirmed, volume-backed breakout. The longer and tighter the squeeze, the stronger the breakout often is.
Q How are Bollinger Bands different from Keltner Channels?
Both are "MA ± width" channels; the difference is the width engine. Bollinger uses standard deviation (more sensitive to volatility spikes, wider swings); Keltner uses ATR (calmer expansion). In violent markets BB opens dramatically; for a smoother envelope, Keltner.
Q What are the MT5 defaults for Bollinger Bands?
20-period SMA middle band with 2.0 standard deviations on PRICE_CLOSE — matching John Bollinger's classic recommendation. For high-volatility instruments (crypto), a larger multiplier (2.5) or longer period (22+) reduces false band touches.
Q Should I sell when price touches the upper band?
No. The meaning of a touch depends on regime: in ranges it is a reversion signal; in trends, price walking the upper band is a strength signature (hold with the trend). Decide whether a trend exists first; only then decide what a touch means.
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