What Are Bollinger Bands? The Volatility Indicator Explained
Bollinger Bands solve a specific problem: how do you know when a price move is "normal" volatility versus something unusual? The bands expand and contract with the market's own volatility — they're essentially a self-adjusting measure of what "stretched" looks like for any given stock at any given time.
The squeeze is the most actionable Bollinger Band signal — when the bands narrow to their tightest point in months, a significant move is imminent in either direction, and the direction of the first breakout from the squeeze often sets the trend for weeks. Price touching the upper band is not automatically a sell signal in a strong uptrend; in trending markets, price can ride the upper band for extended periods. APEX uses Bollinger Band width (the squeeze condition) as part of its volatility and momentum assessment layer in the composite signal.
What Are Bollinger Bands?
Bollinger Bands are three lines plotted on a price chart. The middle band is a 20-period simple moving average (SMA). The upper band is that SMA plus 2 standard deviations. The lower band is that SMA minus 2 standard deviations. The bands automatically widen when price swings are large and narrow when price is calm.
The statistical logic: roughly 95% of price action falls within 2 standard deviations of the mean. So when price touches or breaks the upper or lower band, it's doing something statistically unusual — and that's worth paying attention to.
The Squeeze: The Setup That Traders Love
When the bands come very close together — usually after a long period of low volatility — it's called a squeeze. The market has been coiling like a spring. Historically, squeezes precede significant price moves because volatility tends to cycle: low volatility leads to high volatility, and vice versa.
The squeeze itself doesn't tell you which direction the breakout will go. That's the critical part most beginners miss. A squeeze is a timing signal, not a direction signal. You need something else — trend, volume, RSI, or a catalyst — to determine which way to trade the eventual breakout.
Most traders wait for the breakout candle: price closing outside the band after a squeeze, ideally on above-average volume, before entering. Fakeouts (false breakouts that immediately reverse) are common, which is why volume confirmation matters.
Walking the Band in a Trend
One of the most misunderstood Bollinger Band behaviors: in strong trends, price can "walk" the upper or lower band for weeks. It touches the upper band, pulls back slightly to the middle band, then touches the upper band again. This is not a sell signal — it's a confirmation of strong trend momentum.
Selling every time price touches the upper band in a strong uptrend is a losing strategy. It cuts winners short in the strongest possible market environment. The walk ends when price closes below the middle band — that's when you start questioning the trend.
Bollinger Bands + RSI: A Better Combination
Bollinger Bands alone have a known weakness: they can signal "overbought" conditions in a stock that's simply in a strong uptrend. Pairing them with RSI filters out many false signals. A touch of the upper band with RSI below 70 (not yet overbought) in an uptrend is a very different setup than the same touch with RSI at 82 after a 40% run.
The most reliable mean-reversion signals come when price tags the lower band while RSI is below 30 — that's a double oversold signal in a stock that isn't in a structural downtrend.