get DATEDIFF excluding weekends using sql server

I am using this query to get time taken.

SELECT DATEDIFF(dd, ActualStartDate, ActualCompletionDate) AS TimeTaken
FROM TableName

Now I want to exclude weekends and only include Mon-Fri as days counted.

Example query below, here are some details on how I solved it.

Using DATEDIFF(WK, ...) will give us the number of weeks between the 2 dates. SQL Server evaluates this as a difference between week numbers rather than based on the number of days. This is perfect, since we can use this to determine how many weekends passed between the dates.

So we can multiple that value by 2 to get the number of weekend days that occurred and subtract that from the DATEDIFF(dd, ...) to get the number of weekdays.

This doesn't behave 100% correctly when the start or end date falls on Sunday, though. So I added in some case logic at the end of the calculation to handle those instances.

You may also want to consider whether or not the DATEDIFF should be fully inclusive. e.g. Is the difference between 9/10 and 9/11 1 day or 2 days? If the latter, you'll want to add 1 to the final product.

declare @d1 datetime, @d2 datetime
select @d1 = '9/9/2011',  @d2 = '9/18/2011'

select datediff(dd, @d1, @d2) - (datediff(wk, @d1, @d2) * 2) -
       case when datepart(dw, @d1) = 1 then 1 else 0 end +
      case when datepart(dw, @d2) = 1 then 1 else 0 end

I found when i used this there was a problem when d1 fell on saturday. Below is what i used to correct this.

declare @d1 datetime, @d2 datetime
select @d1 = '11/19/2011' ,  @d2 = '11/28/2011'

select datediff(dd, @d1, @d2) +case when datepart(dw, @d1) = 7 then 1 else 0 end - (datediff(wk, @d1, @d2) * 2) -
 case when datepart(dw, @d1) = 1 then 1 else 0 end +
 case when datepart(dw, @d2) = 1 then 1 else 0 end

BEGIN 
DECLARE @totaldays INT; 
DECLARE @weekenddays INT;

SET @totaldays = DATEDIFF(DAY, @startDate, @endDate) 
SET @weekenddays = ((DATEDIFF(WEEK, @startDate, @endDate) * 2) + -- get the number of weekend days in between
                       CASE WHEN DATEPART(WEEKDAY, @startDate) = 1 THEN 1 ELSE 0 END + -- if selection was Sunday, won't add to weekends
                       CASE WHEN DATEPART(WEEKDAY, @endDate) = 6 THEN 1 ELSE 0 END)  -- if selection was Saturday, won't add to weekends

Return (@totaldays - @weekenddays)

END

This is on SQL Server 2014