What Bollinger Bands actually are
Bollinger Bands were created by John Bollinger in the 1980s. They are three lines drawn on a price chart: a middle band, an upper band, and a lower band. The middle band is a simple moving average, 20 periods by default. The outer two bands are placed a set distance above and below that average, and that distance is what makes the tool useful.
The key idea is that the outer bands are not fixed. They are pinned to volatility, so they breathe in and out as the market gets calmer or wilder. That single property is what separates Bollinger Bands from a plain moving average envelope, and it is the reason a band that looked far away one day can sit right on price the next.
How the bands are built
You never draw the bands by hand, but seeing the shape of the math makes the reading click. The outer bands are the middle average shifted up and down by a multiple of the standard deviation of price, two by default.
- 1. Middle band = a 20-period simple moving average of price. The center of gravity for recent price.
- 2. Outer bands = middle band ± 2 standard deviations of price. Standard deviation is a volatility measure, so the spacing tracks how much price is moving.
- 3. The takeaway = the bands are a volatility envelope. Wild markets push the bands apart; calm markets pull them together.
That is the whole engine. Because standard deviation grows when price swings get bigger, the bands WIDEN when volatility rises and CONTRACT when volatility falls. The distance between the two outer bands is, quite literally, a live picture of how much the market is moving right now.
The squeeze, and what it does and does not tell you
When volatility drops, the bands pull in tight around price. Traders call this a squeeze. A squeeze often comes before a volatility expansion, a stretch where price breaks out of its quiet range and starts moving fast again. Markets tend to alternate between quiet coiling and loud expansion, and the squeeze is the coiling part made visible.
Here is the part that trips people up: the squeeze tells you a move is likely, but it does not tell you the direction. Tight bands are a heads-up that energy is building, not a prediction of up or down. The actual direction only shows once price resolves the range, which is why trading the squeeze means waiting for the break rather than guessing which side it takes.
%B, bandwidth, and mean reversion
Two companion readings make the bands easier to use. %B measures where price sits relative to the bands on a simple scale: at the lower band it reads near 0, at the middle band near 0.5, and at the upper band near 1. Bandwidth measures how far apart the bands are, so a low bandwidth is the numeric version of a squeeze and a high bandwidth marks an already-stretched, volatile market.
People often trade the bands as a mean-reversion tool, expecting price to snap back toward the middle band after tagging an outer one. That read works best in a range-bound market, where price genuinely bounces between the bands. It breaks down in a strong trend, where price can hug one band the whole way. Knowing which environment you are in matters more than the tag itself.
The upper-band-is-not-a-sell trap
The most expensive mistake with Bollinger Bands is a specific one: shorting a strong uptrend just because price touched the upper band. It feels smart, like you are selling into an extreme. In trending names it is the fast way to get run over, because a strong trend will walk the upper band, printing tag after tag while it keeps climbing and stopping out every early short. This is the exact same trap as fading a high RSI reading.
This is the overextension mistake WeTradePro is built to catch. The tool is not there to draw the bands for you; your chart already does that. It is there to flag when you are about to fight a trend because price looks stretched, and to keep you from turning a volatility gauge into a reason to lose money. Context and confirmation, not a single tag, are what keep the bands honest.