Calculating Standard Deviation for Bollinger Bands

Hi all,
I am creating a Python software for Bollinger Bands (as a project). When calculating standard dev, do I use historical volatility? Also, is the time period for standard dev calculation is same as time period for SMA (e.g. 20-day SMA and 20-day standard dev)?
Thanks!
 
Hi all,
I am creating a Python software for Bollinger Bands (as a project). When calculating standard dev, do I use historical volatility? Also, is the time period for standard dev calculation is same as time period for SMA (e.g. 20-day SMA and 20-day standard dev)?
Thanks!

What else would you use?
 
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