Bollinger Bands
Bollinger Bands wrap a moving average in volatility bands that expand and contract. Learn how they show overbought and oversold levels and signal volatility shifts.
Bollinger Bands wrap a moving average in two bands, one above and one below, set a couple of standard deviations away. The bands expand when the market is volatile and contract when it is calm, giving you a live picture of both price extremes and changing volatility.
They are like an elastic channel that stretches and squeezes around price. Let me show you how to read the stretch.
An Elastic Channel
At the center is a moving average, usually 20 periods. Around it, an upper and lower band are drawn at a set distance, typically two standard deviations of recent price. Because standard deviation is a measure of volatility, the bands breathe: they widen when price is swinging wildly and narrow when it is quiet.
Price spends most of its time inside the channel. When it pushes up to the upper band, it is stretched high relative to recent action, a possible overbought signal. When it sags to the lower band, it is stretched low, a possible oversold one. Like a rubber band, price that stretches to an edge often snaps back toward the middle, at least in calm, range-bound markets.
Reading the Bands
Bollinger Bands give two very different kinds of signal, and mixing them up is a common error.
Mean reversion. In a calm, range-bound market, price touching a band often reverts toward the middle. Traders may fade the touch, buying near the lower band and selling near the upper, expecting the rubber band to snap back.
The squeeze. When the bands contract tightly, volatility has dropped to a low, a "squeeze." A squeeze often precedes a big move: calm builds up, then price breaks out sharply in one direction. The squeeze does not tell you which way, only that a surge in volatility is likely coming. This is one of the most valued Bollinger signals, and it connects to the idea of implied volatility being low before it expands.
Riding the band. In a strong trend, price can "walk the band," hugging the upper band all the way up. That is a sign of strength, not a reason to sell.
The Caveat
Bollinger Bands are versatile, but their two signals pull in opposite directions, and knowing which market you are in is everything.
Touching a band is not automatic. In a range, a band touch may mean reversion; in a strong trend, it means momentum, and fading it gets you run over. The exact same event, price hitting the upper band, is a sell signal in one context and a buy-strength signal in another. That is why traders never trade band touches blindly.
The fix is context. Use Bollinger Bands to read whether price is stretched and whether volatility is coiling, then confirm with the trend and momentum tools before acting. Read that way, they are a rich, two-in-one gauge of price extremes and volatility.
- Bollinger Bands wrap a moving average in volatility bands.
- The bands widen and narrow with volatility.
- A squeeze (tight bands) often precedes a big move.
- A band touch means reversion in a range but strength in a trend.
Pop Quiz
Three quick questions to see what stuck. Pick an answer and the explanation shows up right away.
What makes Bollinger Bands widen and narrow?
The bands are set by standard deviation, so they widen in volatile markets and narrow in calm ones.
What does a Bollinger squeeze often precede?
Tight bands signal low volatility that often builds up before a sharp move, though not the direction.
Price touches the upper band. Is that a sell signal?
In a range a touch may revert, but in a strong trend price can walk the band higher, so context matters.
Bottom Line
Bollinger Bands drape a moving average in an elastic channel that breathes with volatility. Price touching a band flags a stretch, a tightening squeeze warns a big move is coming, and the bands' width itself is a live read on how wild or calm the market is.
Their power and their trap are the same: a band touch means reversion in a range but strength in a trend. Read the context first, confirm with the trend, and Bollinger Bands become a rich two-in-one view of price extremes and volatility.
Keep going: the center line is a moving average, the squeeze connects to implied volatility, and momentum companions are the RSI and stochastic.