Who created Bollinger Bands and what do they measure?

Bollinger Bands were created by American technical analyst John Bollinger in the early 1980s. The indicator measures volatility relative to a moving average. The middle band is a simple moving average (typically 20 periods), and the upper and lower bands are placed two standard deviations above and below the middle. As volatility expands, the bands widen; as volatility contracts, they narrow. Bollinger Bands therefore serve as a dynamic, volatility-adjusted envelope around price.

Does price touching the upper band mean a stock is overbought?

Not necessarily. While price touches of the upper band have historically been described as overbought conditions and lower band touches as oversold, John Bollinger himself emphasised that band touches by themselves are not signals. In strong trends, price can "walk the upper band" for extended periods — repeatedly tagging the upper band without reversing. Likewise, price can walk the lower band in strong downtrends. Band touches must be interpreted in context with other indicators.

What is the difference between Band Width and %B?

Both are companion indicators derived from Bollinger Bands. Band Width measures the distance between the upper and lower bands, normalised by the middle band — it is a single number that reflects the current width of the bands relative to price. %B (percent B) measures where the current price sits within the bands — 0 means price is at the lower band, 1.0 means at the upper band, 0.5 means at the middle band, and values outside this range mean price has exited the band envelope. Band Width is a volatility gauge; %B is a position gauge.

Bollinger Bands: How to Use Volatility-Based Trading Bands on Indian Stocks

Q: What is the Bollinger Squeeze?

The Bollinger Squeeze is a condition where the upper and lower bands contract significantly toward the middle band, indicating that volatility has fallen to a relatively low level. Historically, periods of unusually low volatility have often preceded periods of higher volatility — though the squeeze gives no information about the direction of any subsequent move. It is a context indicator, not a directional signal.

Origin: John Bollinger and the volatility envelope

Bollinger Bands were developed by American technical analyst John Bollinger in the early 1980s. Bollinger was working as a market technician at the time and observed that fixed percentage envelopes — bands placed a fixed percent above and below a moving average, which were popular in the 1970s — failed to adapt to changing volatility. A 5% envelope that worked during a calm period was useless during a turbulent one, and vice versa.

Bollinger's insight was to make the envelope width itself a function of recent volatility. By using standard deviation — a statistical measure of dispersion — instead of a fixed percent, the bands automatically expand when prices become more volatile and contract when they calm down. This made the resulting envelope self-adjusting and broadly comparable across different securities and different volatility regimes.

For the underlying mathematics, see our moving averages guide.

The three bands: structure and formula

A standard Bollinger Bands plot consists of three lines drawn on top of price.

Middle band = SMA(20) of close
Upper band = Middle band + (2 × σ)
Lower band = Middle band − (2 × σ)

Where σ is the standard deviation of closing prices over the same 20-period window. The default settings — 20 periods for the moving average and 2 standard deviations for the bands — are the values Bollinger himself recommended after extensive back-testing.

Statistically, if price changes were normally distributed (which they are not in financial markets), about 95% of observations would fall within two standard deviations of the mean. In practice, real price data has fat tails — extreme moves are more common than the normal distribution would suggest — so the "95%" is an approximation, not a guarantee.

What Bollinger Bands actually measure

Bollinger Bands measure two things simultaneously:

Trend direction — through the slope and position of the middle band, which is just the underlying moving average.
Volatility — through the distance between the upper and lower bands. Wide bands describe a high-volatility regime; narrow bands describe a low-volatility regime.

This dual nature is why Bollinger Bands have remained popular for four decades. Unlike a single-purpose indicator, they communicate both directional and volatility information in one plot.

The Bollinger Bounce concept

In range-bound markets — when price is oscillating without a clear trend — Bollinger Bands have historically acted as a mean-reversion envelope. Price moves toward one of the outer bands, stalls, and reverts back toward the middle band. This pattern has been called the Bollinger Bounce.

The bounce reflects the statistical observation that prices tend to oscillate around their moving average. When price stretches a distance equal to two standard deviations away from the mean, that stretch is, by construction, large relative to recent volatility — and historically has often been followed by a return toward the mean.

Crucially, the Bollinger Bounce only describes range-bound conditions. In trending markets, the bounce concept fails — price can stay near or beyond an outer band for extended stretches as the trend unfolds.

The Bollinger Squeeze

The Bollinger Squeeze is one of the most discussed features of the indicator. A squeeze occurs when Band Width — the distance between the upper and lower bands — contracts to a relatively low level. Visually, the bands appear to pinch tightly around price.

Squeezes are a direct expression of low volatility. When recent price changes have been small, the standard deviation falls, and both bands move closer to the middle band. Historically, periods of unusually low volatility have often been followed by periods of higher volatility — markets do not stay quiet forever. This observation is sometimes summarised as "volatility clusters and mean-reverts."

A common misconception is that a squeeze predicts the direction of the subsequent move. It does not. A squeeze is a context indicator — it describes that volatility has compressed, and historically a subsequent expansion is common — but the direction of that expansion must be inferred from other lenses such as price structure, volume, or higher-timeframe context.

Walking the Bands in strong trends

One of the most important nuances of Bollinger Bands — and one that John Bollinger has emphasised in his own writings — is that band touches are not automatic reversal signals. In strong trends, price can repeatedly touch and even close above the upper band (in an uptrend) or below the lower band (in a downtrend) without reversing. This phenomenon is called walking the bands.

Walking the upper band has historically been observed in strongly trending Indian large-caps during multi-month rallies. Each touch of the upper band, taken in isolation, would have been called "overbought" by traditional band-bounce logic — but the upward trend continued anyway. The same applies to walking the lower band in declining markets.

The practical lesson: a band touch tells you where price sits relative to recent volatility, not whether the trend is about to reverse. Distinguishing between mean-reverting conditions (where band bounces are more reliable historically) and trending conditions (where walking the bands is common) requires additional analysis.

Historical examples on Indian markets

The patterns below describe what has been observed historically on Indian indices and stocks. They are illustrative observations, not forecasts.

Nifty 50 — 2008 global financial crisis. During the sharp decline of 2008, Bollinger Bands on the Nifty 50 daily chart widened dramatically as standard deviation expanded with volatility. Price walked the lower band for extended stretches as the downtrend persisted, and only after volatility began to compress — visible as the upper and lower bands beginning to contract — did mean-reversion bounces back toward the middle band begin to hold.

Nifty 50 — March 2020 COVID crash. The pandemic crash produced one of the most extreme Bollinger Band expansions in Indian market history. Prior to the decline, the bands had compressed during the late 2019 and early 2020 consolidation — historically a textbook squeeze. The subsequent move was sharp and downward. As price stabilised through April and May, Band Width began to contract again, and the recovery took shape with a gradual narrowing of the volatility envelope.

2024 election volatility. The Indian general election of 2024 produced a notable single-day move on the Nifty 50 that stretched price several standard deviations beyond the upper-band-equivalent zone before reverting. The Bollinger Bands widened sharply that day and then contracted over the following weeks as volatility normalised — a classic post-event volatility decay.

Companion indicators: Band Width and %B

John Bollinger also developed two derivative indicators that are often plotted alongside the bands themselves.

Band Width. A single-line indicator measuring the distance between the upper and lower bands, normalised by the middle band:

Band Width = (Upper − Lower) / Middle

Plotted as a line below price, Band Width makes squeezes and expansions easy to spot — local minima in Band Width identify historical squeezes; local maxima identify historical volatility peaks.

%B (percent B). A position indicator showing where price sits within the bands:

%B = (Price − Lower) / (Upper − Lower)

A %B value of 1.0 means price is at the upper band, 0 means at the lower band, 0.5 means at the middle band. Values above 1 or below 0 mean price has exited the band envelope — historically associated with extreme stretch in the prevailing direction.

Combining Bollinger Bands with other indicators

Like all indicators, Bollinger Bands are most informative when combined with complementary lenses.

Volume. A breakout above the upper band accompanied by expanding volume has historically been interpreted as more meaningful than the same breakout on declining volume. Volume measures participation; participation adds context to a band move.
RSI. When price tags the upper band while RSI shows a divergence, historical mean-reversion outcomes have been more frequent than band touches without RSI confirmation. For more, see our RSI guide.
Support and resistance. Bollinger Band touches that coincide with horizontal support or resistance levels have historically been considered higher-context observations. See our support and resistance guide.

Parameter tuning: 20-day default and alternatives

The defaults of 20 periods, 2 standard deviations are the most commonly used settings and are the values built into virtually every charting platform used in Indian markets. They represent roughly one trading month of data with a band envelope wide enough to contain the bulk of normal price activity.

Some alternative configurations are seen in practice:

10-period bands — Used by very short-term participants who want the bands to respond more quickly to recent price changes. The trade-off is more whipsaw — the shorter window makes the bands jumpier.
50-period bands — Used by positional analysts who want a slower envelope that reflects multi-month volatility. The trade-off is later confirmation of regime changes.
2.5 or 3 standard deviation bands — Wider envelopes that reduce the frequency of band touches. Useful in very volatile securities where 2σ bands are tagged too often to be meaningful. Statistically, 3σ bands enclose roughly 99% of normally-distributed observations — though, again, real markets are not normally distributed.

Limitations of Bollinger Bands

Lagging indicator. The middle band is a moving average and therefore lags. The standard deviation calculation is also based on past prices.
Assumption of normality. The 2σ envelope assumption that 95% of data falls inside the bands is based on the normal distribution. Real market returns have fat tails — extreme moves are more common than the normal distribution predicts.
Band touches are not signals. As Bollinger himself emphasised, a touch of the upper or lower band by itself does not mean price will reverse. Strong trends can walk the bands for long periods.
Squeezes lack direction. The squeeze indicates that volatility has compressed but says nothing about the direction of any subsequent expansion.
Parameter sensitivity. Changing the lookback or the number of standard deviations changes the signals. There is no universally optimal configuration.