declare @FirstPayDate	 datetime
set @FirstPayDate	= '20100101'

select
	*,
	FirstPayDateOfCurrentQuarter =
	dateadd(dd,(datediff(dd,@FirstPayDate,dateadd(dd,13,
	dateadd(qq,datediff(qq,@FirstPayDate,Date),@FirstPayDate)))/14)*14,@FirstPayDate)
from
	(
	select Date = convert(datetime,'20100727')	union all
	select Date = convert(datetime,'20100827')	union all
	select Date = convert(datetime,'20101001')
	) a
order by
	a.Date

Date                     FirstPayDateOfCurrentQuarter
-----------------------  ----------------------------
2010-07-27 00:00:00.000  2010-07-02 00:00:00.000
2010-08-27 00:00:00.000  2010-07-02 00:00:00.000
2010-10-01 00:00:00.000  2010-10-08 00:00:00.000

(3 row(s) affected)