>I would expect the date
>
>2011-09-11 14:01:37.963
>
>minus 4 years
>
>2007-09-11 14:01:37.963
>
>then the previous 1st October is 2006

I see, I think I misread the original requirement.

In this case:

DECLARE @testdate datetime

SET @testdate = DATEADD(MONTH,-2,CURRENT_TIMESTAMP )
SELECT CASE WHEN RIGHT(CONVERT(VARCHAR(10), @testdate, 112) ,4) >'1001' 
                THEN CONVERT(datetime,LTRIM(YEAR(@testdate)-4) + '1001')

         ELSE CONVERT(datetime,LTRIM(YEAR(@testdate)-5) + '1001') END