Weekday Algorithm

select getdate() as 'Current Date'

,datepart(dw,getdate()) as 'Day of Week (Sun=1)'

,dateadd(day,-(datepart(dw,getdate()) - 1),getdate()) as 'FirstDay' 

,dateadd(day,(7 - datepart(dw,getdate())),getdate()) as 'EndDay'