Bollinger Bands are a technical analysis indicator developed by John Bollinger in the 1980s. The tool consists of three lines plotted on a price chart: a middle band (20-day simple moving average) and two outer bands positioned two standard deviations above and below it. As price volatility changes, the bands expand and contract, giving investors a visual representation of market conditions at a glance.
How It Works
The middle band tracks the average price over 20 days. The upper and lower bands adjust automatically based on price volatility—when volatility increases, the bands widen; when it decreases, they narrow. This dynamic nature makes Bollinger Bands responsive to changing market conditions. Prices that touch or move beyond the outer bands often signal extreme conditions, while prices bouncing between the bands suggest normal trading ranges.
Why It Matters for Investors
For active traders and portfolio managers, Bollinger Bands serve multiple purposes. They help identify volatility spikes that might precede significant price moves. When bands squeeze together (low volatility), it often indicates a breakout may be coming. When price approaches the upper band, assets may be overbought; when approaching the lower band, they may be oversold. This information helps with entry and exit timing, risk management, and positioning decisions. The indicator works across all timeframes—from day trading charts to longer-term investment analysis.
Example
Imagine a tech stock trading around $100 with Bollinger Bands set at $95 (lower), $100 (middle), and $105 (upper). If the stock suddenly spikes to $110, it's trading above the upper band, signaling potential overbought conditions where a pullback might occur. Conversely, if it drops to $92, it's below the lower band, suggesting oversold conditions where a bounce could happen. A savvy investor might use these signals to consider taking profits on strength or initiating positions on weakness, depending on their strategy.
Key Takeaways
- Bollinger Bands measure volatility and identify extreme price conditions relative to recent trading history
- The bands expand during high volatility and contract during calm markets, helping you spot periods of potential breakouts
- Prices touching upper or lower bands don't guarantee reversals—they signal conditions worth monitoring alongside other indicators
- Most effective when combined with fundamental analysis and other technical tools rather than used in isolation