Bollinger Bands

Bollinger Bands are a technical analysis tool that plots price volatility around a moving average using three lines. The bands widen during high volatility and narrow during low volatility, helping traders spot potential overbought or oversold conditions.

• Middle band: 20-day simple moving average (SMA)
• Upper and lower bands: placed 2 standard deviations above and below the SMA
• Narrow bands signal low volatility; wide bands signal high volatility
• Best used alongside other indicators, such as RSI or MACD, rather than alone

Bollinger Bands work by plotting three lines around an asset's price to track volatility and potential reversals. The middle band tracks the average price, while the upper and lower bands expand and contract based on how much the price moves.

Bollinger Bands tell you the current level of market volatility and highlight potential entry or exit zones. Narrow bands indicate low market volatility, while wide bands indicate high market volatility. When the price moves closer to or crosses the upper band, it may signal that the asset is overbought. When the price moves closer to the lower band, it may signal that the asset is oversold.

Bollinger Bands work best as a confirmation tool, not a standalone signal. Experienced traders combine Bollinger Bands with other technical indicators and fundamental analysis methods before acting on a signal. Relying on one indicator alone increases the chance of misreading a signal and taking a loss.

You calculate Bollinger Bands using a 20-day simple moving average and the price's standard deviation over the same period. The three lines follow a fixed formula:

1. Calculate the middle band as the 20-day simple moving average (SMA) of the closing price.
2. Calculate the standard deviation of price over the same 20-day period.
3. Add 2 times the standard deviation to the middle band to get the upper band.
4. Subtract 2 times the standard deviation from the middle band to get the lower band.

The securities and price levels discussed in this article are for example purposes only and not a recommendation.

A trader analysing a stock's price over a 20-day period plots the middle line as the 20-day SMA, with the upper and lower bands placed 2 standard deviations away. When the price stays within the bands, the market shows stable conditions with low volatility. A move beyond either band signals a rise in volatility.

Traders often treat the price touching the upper band as a potential overbought signal, suggesting a possible sell opportunity. Conversely, the price reaching the lower band may indicate the stock is oversold, pointing to a potential buying opportunity. This example is illustrative only and not a recommendation to trade any specific security.

Bollinger Bands carry several limitations that traders should account for before relying on them. The table below sets out each limitation and why it matters.

Bollinger Bands work well alongside the Relative Strength Index (RSI), Moving Average Convergence Divergence (MACD), and other momentum or volume-based indicators to validate signals. Using band width as the only decision factor increases the risk of a false signal, so pairing Bollinger Bands with a second indicator strengthens the analysis.

The effectiveness of any combination depends on current market conditions and the trader's own strategy. Backtesting a chosen combination before live trading helps confirm whether it works reliably for a given asset.

Bollinger Bands' accuracy varies case by case and depends on the indicators and market conditions used alongside them. Combining Bollinger Bands with tools such as trendlines, candlestick charts, RSI, and fundamental analysis of a company's financial statements tends to improve signal reliability.

Bollinger Bands can be relatively accurate for identifying potential entry or exit points, but no technical indicator guarantees a correct signal. Traders need to adjust their approach as market conditions and asset prices change, and treat every signal as one input among several rather than a standalone decision rule.

Bollinger Bands measure price volatility using a moving average and two surrounding bands, helping traders spot potential overbought or oversold conditions. The indicator works best combined with tools like RSI or MACD, since Bollinger Bands alone can produce false signals in sideways or strongly trending markets. Understanding both the calculation and the limitations of Bollinger Bands helps traders use the tool as one part of a broader, well-researched strategy.