Question: how to calculate business days on tableau?
Answer: (DATEDIFF('day',[Day1],[Day2]) - (7-DATEPART('weekday',[Day1])) - DATEPART('weekday',[Day2]) ) / 7*5. + MIN(5,(7-(DATEPART('weekday',[Day1])))) ... 
(DATEDIFF('day',[Day1],[Day2])
- (7-DATEPART('weekday',[Day1]))
- DATEPART('weekday',[Day2])
+ MIN(5,(7-(DATEPART('weekday',[Day1]))))
+ MIN(5,(DATEPART('weekday',[Day2])-1))