xxxxxxxxxx
select DATEADD(wk, DATEDIFF(wk,0,
dateadd(dd,6-datepart(day,getdate()),getdate())
), 0)
--Change getdate to your variable
xxxxxxxxxx
select FirstDayMonth = DATEADD(month, DATEDIFF(month, 0, getdate()), 0),
FirstDayWeek = DATEADD(week, DATEDIFF(week, -1, getdate()), -1)