Need a way to exclude holidays from my weekly incident volume average

Content

I have a custom report that contains these columns :

Week start: date_group(stats.stat_date, $date_grp_param) 

Total chats: sum( stats.new_incidents )

Daily Average: sum(stats.new_incidents) / 5

 

I want to have my last column, daily average, account for when a day that week is a holiday. Any suggestions on a good way to do this that wouldn't be too much of a performance drain? 

Version

May 2016