Trends/Volatility and bands

Bollinger bandwidth

A single number for how wide the Bollinger bands are, as a percent of the middle line.

Volatility and bandsBest on 6M, 1Y, 3YAlso called BBW

Illustration of the Bollinger bandwidth shape. It is a sketch, not real price data.

What it shows

Bandwidth is (upper band − lower band) ÷ middle line. It does not show direction, only how wide the bands are. A low value means price has been quiet. A high value means price has been swinging widely.

Tracking it over time shows when volatility is high or low compared with the past.

How we find it

The same code that draws it on your chart follows these steps, with the same result every time.

Compute the Bollinger bands (20, 2).
Bandwidth = (upper − lower) ÷ middle.
Plot it under the price.
Mark the lowest and highest values in the period.

Starting values: Length 20; Width 2 standard deviations. These are proposed and will be tuned on real price data before launch.

How to read it

The panel shows band width over time.
A falling line means the bands are narrowing.
A rising line means the bands are widening.

Status labels you may see

Label	What it means
Narrow	Bandwidth is in the lowest 20% of the period.
Normal	Between the 20th and 80th percentiles.
Wide	Bandwidth is in the highest 20% of the period.

What cancels it

Nothing cancels it.

What traders check next

How low it has been before.
What price did after past lows.
Whether volume changed.

Limits

It shows volatility, not direction.
Low values can last a long time.
Needs a long history to judge.

Try it in forecastviz

Open any ticker and choose Volatility and bands → Bollinger bandwidth in the left menu.
Switch between 6M, 1Y, 3Y to see how the picture changes.
Compare with Bollinger squeeze and Bollinger bands on the same chart.

Open on a ticker

Questions

Is low bandwidth a signal?

It is a fact about calm. We make no claim about what follows.

What is a normal level?

It differs by stock, which is why we compare with the stock's own history.