DATE DIFFRENCE in MS SQL

Declare

    @workingDays int,
    @Count int,
@totWekends int,
    @startdate datetime = getdate(),
    @enddate datetime = getdate()+6

set @Count=6+1;

  set @workingDays= (DATEDIFF(dd, @StartDate, @EndDate) + 1) -(DATEDIFF(wk, @StartDate, @EndDate) * 2)
  -(case datepart(dw, @StartDate)+@@datefirst when 8 then 1 else 0 end)
  -(case datepart(dw, @EndDate)+@@datefirst when 7 then 1 when 14 then 1 else 0 end)

set @totWekends=@Count-@workingDays
select  CONVERT(VARCHAR(10),DATEADD(day,@workingDays+@totWekends,getdate()),103) AS LastDate