Dynamic Forumlas based on Dropdown
 

The following is an abstract of a forumla i'm working with to summarize
points in column BB (which is for January).

{=SUM(('Everyone FCST'!BB1:BB20000.1))}

If I add a drop down in the excel sheet so users can change columns to
diffferent months (columns BC, BD, BE, etc.) is there a way the forumla will
automatically change to search the newly selected column. Example:

{=SUM(('Everyone FCST'!BC1:BC20000.1))}
Thanks so much for any help anyone can provide!!!!