What Are Bollinger Bands?
Bollinger Bands are a volatility indicator created by John Bollinger in the 1980s. They consist of three lines plotted on a price chart: a middle band (a simple moving average), an upper band (the moving average plus a set number of standard deviations), and a lower band (the moving average minus the same number of standard deviations).
The standard settings use a 20-period SMA with bands set at 2 standard deviations. The key insight of Bollinger Bands is that they adapt to market conditions — when volatility increases, the bands widen; when volatility decreases, the bands contract. This dynamic behavior makes them uniquely useful for gauging whether current price action is "normal" or extreme.
How to Read Bollinger Bands
The three bands create a visual channel around the price. Here is what to look for:
- Price near the upper band — The stock is trading at the high end of its recent range. In a strong uptrend, the price can "walk" along the upper band for extended periods. In a range-bound market, touching the upper band may signal short-term overbought conditions.
- Price near the lower band — The stock is at the low end of its range. Similar to the upper band, a touch of the lower band does not automatically mean the stock will bounce — context matters.
- Price at the middle band — The 20-day SMA acts as a dynamic support or resistance level. In uptrends, the price often bounces off the middle band. In downtrends, the middle band can act as resistance.
- Band width — Wide bands indicate high volatility; narrow bands indicate low volatility. The relative width is more important than the absolute width.
The Bollinger Squeeze
The Bollinger Squeeze is one of the most watched setups among technical traders. It occurs when the bands contract to their narrowest point in several weeks or months, indicating that volatility has compressed significantly.
The theory behind the squeeze is simple: markets cycle between periods of low volatility (consolidation) and high volatility (expansion). After an extended period of low volatility, a breakout often follows. Traders watch for the squeeze and then trade in the direction of the subsequent breakout.
However, the squeeze only tells you that a move is likely coming — it does not tell you which direction. This is why many traders combine the squeeze with directional indicators like MACD or watch for a volume spike on the breakout to determine whether to go long or short.
Bollinger Band Trading Strategies
Mean Reversion (Range-Bound Markets)
In sideways markets, prices tend to oscillate between the upper and lower bands. A mean reversion strategy involves buying when the price touches or dips below the lower band and selling when it reaches the upper band. The middle band serves as the initial target.
This strategy works best when the bands are relatively flat (not trending sharply up or down) and the stock is not in a strong directional trend. Using RSI as confirmation — buying only when both the price touches the lower band and RSI is below 30 — can improve the hit rate.
Trend Following (Trending Markets)
In strong trends, the price can ride along the upper band (uptrend) or the lower band (downtrend) for extended periods. Rather than fading these moves, trend-following traders look to enter pullbacks to the middle band in the direction of the trend.
For example, in an uptrend where the price is consistently near the upper band, a pullback to the 20-day SMA (middle band) can be an entry opportunity. If the middle band holds as support, the uptrend may continue. If it breaks below the middle band, the trend may be weakening.
Combining Bollinger Bands with Other Indicators
Bollinger Bands are most powerful when used alongside other technical tools:
- Bollinger Bands + RSI — When the price touches the lower band and RSI is below 30, it is a stronger oversold signal. When the price touches the upper band and RSI is above 70, it is a stronger overbought signal.
- Bollinger Bands + MACD — A Bollinger squeeze followed by a MACD crossover can confirm the direction of the breakout.
- Bollinger Bands + Volume — Breakouts from squeezes on high volume are more likely to follow through than those on light volume.
- Bollinger Bands + Moving Averages — The longer-term MA150 or MA200 can provide the broader trend context, while Bollinger Bands handle the shorter-term volatility picture.
Limitations of Bollinger Bands
Like all technical indicators, Bollinger Bands have limitations:
- They are a lagging indicator — the bands react to price, they do not predict it.
- In strong trends, the price can stay at the upper or lower band for a long time, making mean reversion signals premature.
- The standard 20-period, 2-standard-deviation settings may not suit all markets or timeframes. Some traders adjust these based on the asset they are trading.
- A squeeze does not predict direction — you still need a directional signal to decide whether to go long or short.
Key Takeaways
- Bollinger Bands measure volatility by plotting bands at 2 standard deviations from a 20-day moving average.
- The bands expand during volatile periods and contract during quiet periods.
- The Bollinger Squeeze signals that a significant price move is likely — but not the direction.
- In range-bound markets, the bands can identify overbought and oversold conditions.
- In trending markets, the middle band acts as dynamic support or resistance.
- Combining Bollinger Bands with RSI, MACD, or volume analysis improves signal quality.