add holidays to a custom date

Hello! We use a custom calculated 'real due on' date for many of our tasks. I'd like for this to account for holidays as well. Here is the Text, any ideas how to incorporate holidays into this?

displayname=Real Due On

linkedname=direct

namekey=handoffDate

querysort=handoffDate

textmode=true

valueexpression=ADDWEEKDAYS({handoffDate},{durationMinutes}/480)

valueformat=HTML