# Charts

## Bollinger Band (BBANDS)

### Description

The Bollinger Band study created by John Bollinger plots upper and lower volatility bands around the price of the instrument. The width of the bands are based on the standard deviation of the user defined price from a moving average of n-periods.

### Formula

$Middle\;Band = n-period\;moving\;average$

$Upper\;Band = Middle\;Band\;+\;\left ( y \times n-period\;Standard\;Deviation\right )$

$Lower\;Band = Middle\;Band\;-\;\left ( y \times n-period\;Standard\;Deviation\right )$

where:

$Standard\;Deviation = \sqrt{d}$

with

$d = \frac{(P_{1}-MA)^{2}+(P_{2}-MA)^{2}+...+(P_{n}-MA)^{2}}{n}$

where

$P_{n} =\;the\;user\;defined\;bar\;value\;of\;the\;n^{th}\;bar$

$MA =\;the\;user\;defined\;n-period\;moving\;average$