Bollinger Bands Explained: Squeeze, Band Walk and Mean Reversion

Pull up almost any chart on an Indian trading screen and you’ll find Bollinger Bands on it. You’ll also find plenty of people reading them wrong. This is Bollinger Bands explained from scratch: how the bands are built, the three main ways traders use them, and the traps that catch beginners.

In this article

1. Bollinger Bands explained: what you’re looking at
2. How the bands are worked out
3. Use 1: The Bollinger squeeze
4. Use 2: The band walk (riding a trend)
5. Use 3: Mean reversion in a range
6. Trend or range? Working out which setup fits
7. Pairing Bollinger Bands with other tools
8. Settings: should you tweak 20 and 2?
9. Where Bollinger Bands fall short
10. A checklist before you act on a band signal
11. Mistakes that keep showing up
12. Trying Bollinger Bands on Indian stocks
13. Frequently asked questions
14. What to take away

Bollinger Bands explained: what you’re looking at

Investopedia credits John Bollinger with developing the bands in the 1980s. They measure an asset’s volatility by drawing bands two standard deviations either side of a simple moving average.

You get three lines:

• Middle band: usually a 20-day simple moving average (SMA) of closing prices.
• Upper band: the middle band plus two standard deviations.
• Lower band: the middle band minus two standard deviations.

Standard deviation goes up when prices swing harder, so the bands widen when things get volatile and narrow when they calm down. That width adjusting on its own is the whole point of the tool.

How the bands are worked out

You won’t ever have to calculate them yourself, since every charting platform has them built in. Still, knowing the maths makes it easier to trust what’s on screen.

1. Take the last 20 closing prices and average them. That’s your middle band.
2. Find the standard deviation of those 20 closes. It tells you how far prices usually sit from the average.
3. Multiply the standard deviation by 2.
4. Add that to the middle band to get the upper band, and subtract it to get the lower band.
5. Do it again each day as a fresh close comes in and the oldest one falls away.

A quick example

Say a stock’s 20-day average close is Rs 500 and its standard deviation is Rs 10. These numbers are invented just to show the working.

• Upper band = 500 + (2 × 10) = Rs 520
• Lower band = 500 − (2 × 10) = Rs 480

Now suppose volatility doubles and the standard deviation becomes Rs 20. The bands stretch out to Rs 540 and Rs 460, even though the average is still Rs 500.

The “95%” idea, and why we’d go easy on it

Investopedia explains that two-standard-deviation bands lean on the statistical rule that roughly 95% of data points fall within two standard deviations of the mean when data is normally distributed.

Stock prices, though, are not neatly normally distributed. Sharp moves turn up far more often than a textbook bell curve would suggest. So read the bands as a guide to what’s relatively high or low, not a promise that price will stay inside them.

Bollinger Bands don’t tell you where price will go. They tell you whether today’s price is stretched compared with its own recent behaviour.

Use 1: The Bollinger squeeze

Investopedia points out that narrow bands signal lower volatility, and that this can mean “a significant price move could be imminent”. Traders call this a squeeze.

The reasoning is straightforward. Markets swing between quiet spells and busy ones, and after a long, tight range, volatility usually picks up again.

How traders handle a squeeze

1. Spot it: the bands are clearly the tightest they’ve been in several weeks or months.
2. Wait for the break: a decisive close outside the upper or lower band hints at which way the expansion will go.
3. Check volume: a breakout on rising volume is more trustworthy than one on thin volume.
4. Place a stop: many traders use the other side of the squeeze range, or the middle band.

The catch: a squeeze often throws up a false move first, the so-called “head fake”, before the real one shows up. Waiting for a close instead of jumping on an intraday spike weeds out some of these.

Use 2: The band walk (riding a trend)

A classic beginner error is selling every time price taps the upper band. In a strong uptrend, price can “walk” up the upper band for days or even weeks, touching it or closing near it again and again.

What a healthy band walk looks like:

• The middle band is clearly sloping up (or down, in a downtrend).
• Pullbacks find support around the middle band instead of sliding all the way to the lower band.
• The bands are opening up, not squeezing in.

Investopedia notes that the middle band’s direction is itself useful for reading the trend: a rising middle band suggests an uptrend, and a falling one suggests the reverse.

During a band walk, touching the upper band is a sign of strength, not a reason to go short.

A touch of the upper band is not a sell signal by itself. In a strong trend, it’s often a sign the trend is still in charge.

Use 3: Mean reversion in a range

When a stock is drifting sideways and the middle band is more or less flat, the bands can mark out the edges of that range.

Investopedia describes how many traders treat the zone near the upper band as possible overbought territory and resistance, and the zone near the lower band as possible oversold territory and support.

A basic mean-reversion setup

• Condition: flat middle band, no strong trend.
• Entry idea: price closes below the lower band and then closes back inside it.
• Target: the middle band, maybe booking part of the position there.
• Stop: below the recent low.

That “close back inside” condition is important. Buying simply because price has dropped below the lower band can mean catching a falling knife during a breakdown.

Trend or range? Working out which setup fits

Clue	Trending (band walk)	Ranging (mean reversion)
Middle band	Clearly sloping	Roughly flat
Band width	Expanding	Stable or narrowing
Pullbacks	Hold near the middle band	Swing from band to band
Upper-band touch means	Strength	Possible stretch

Pairing Bollinger Bands with other tools

According to Investopedia, Bollinger Bands do their best work as a secondary indicator that confirms what tools like RSI and MACD are saying.

• RSI: a lower-band touch with a bullish RSI divergence is a stronger reversal hint than either one by itself.
• Volume: a squeeze breakout carries more conviction when volume jumps.
• Support and resistance: a band touch that coincides with a known horizontal level counts for more.
• Candlesticks: a hammer at the lower band or a shooting star at the upper band adds confirmation.

Settings: should you tweak 20 and 2?

Investopedia notes that the standard 20-day SMA and two standard deviations won’t fit every trading situation, and most platforms let you change both.

• Shorter period (say 10): the bands react faster, which suits short-term traders, but you get more noise.
• Longer period (say 50): smoother bands that work for positional traders.
• More standard deviations: fewer touches, so fewer signals.

Whatever you settle on, test it on old charts of the stocks you actually trade before putting real money behind it.

Where Bollinger Bands fall short

Investopedia lists a few limitations:

• They’re a lagging indicator, reacting to price instead of predicting it.
• They can throw up false signals in very volatile spells when the bands blow out.
• The default settings won’t suit every market or timeframe.

We’d add the most common real-world problem: reading the same signal the same way in every market condition. The upper band means one thing in a trend and something quite different in a range.

A checklist before you act on a band signal

1. Is the middle band sloping or flat? That tells you whether you’re in a trend or a range.
2. Are the bands widening or narrowing?
3. Does the signal line up with a support or resistance level?
4. Is volume backing the move?
5. Where’s your stop-loss, and is the potential reward worth the risk?

If you can’t answer all five, you’re usually better off waiting for a cleaner setup.

Mistakes that keep showing up

1. Shorting every upper-band touch in an uptrend.
2. Buying every lower-band touch in a downtrend.
3. Trading a squeeze before the breakout is confirmed.
4. Ignoring volume and the broader market’s direction.
5. Skipping the stop-loss because “price always returns to the middle band”. It doesn’t always.

Trying Bollinger Bands on Indian stocks

Open a daily chart of any liquid Nifty 50 stock in your broker’s charting tool and add Bollinger Bands on default settings. Then scroll back over the past year and mark:

• Every squeeze, and which direction price broke afterwards.
• Every band walk, and where it ran out.
• Every range, and how often the lower band held.

You’ll learn more from this than from any list of rules. It becomes obvious pretty fast that context, trend or range, decides what a band touch means.

If you want a structured free course, Zerodha Varsity’s technical analysis module is a sensible next stop.

Frequently asked questions

Are Bollinger Bands good for intraday trading?

You can use them on intraday charts like 5-minute or 15-minute timeframes, but the signals get noisier. Many intraday traders pair them with VWAP and volume.

Which is better, Bollinger Bands or RSI?

They measure different things. Bollinger Bands show volatility and where price sits relative to recent levels, while RSI tracks momentum. Together, they fill in each other’s gaps.

Does a close outside the band mean a reversal?

Not necessarily. In a strong trend, closes outside the band can carry on for days. Get confirmation before assuming a turn.

What to take away

• Bollinger Bands are a 20-day SMA with bands two standard deviations above and below it.
• Tight bands (a squeeze) often come before a big move. Wait for confirmation.
• In a trend, price can walk the band, so a touch shows strength.
• In a range, the bands can mark mean-reversion zones.
• Use them with RSI, MACD, volume and price levels, never on their own.

To round out your toolkit, read our guide to technical analysis for Indian stocks and our primer on candlestick patterns for beginners.

This article is for educational purposes only and is not investment advice.