Do I include the square footage of my basement when calculating the total square footage of my house for home office?

Generally, if the space is not heated and cooled, then you would not include it as part of your total square feet.

If your home office is located in the basement area or if you are claiming a section of the basement for storage in conjunction with your home office, then you would include that area being used as part of the total. 

My basement is finished, heated, and cooled.  It's also a walk-out basement, but I don't use it for storing supplies and my office is on the main level.  Do I include the basement in my total square footage?