DECLARE @FirstOfMonth datetime
-- Calculate the first of the month
@FirstOfMonth = DATEADD(mm,DATEDIFF(mm,0,EndDate),0)
select Claim_Reference, Claim_Registered_Date, EndDate,
CASE
WHEN overall_stat = "Outstanding"
     AND Claim_Registered_Date >= @FirstOfMonth
		THEN "01 - Up to 1 Month"

WHEN overall_stat = "Outstanding"
     AND Claim_Registered_Date >= DATEADD(mm, -2, @FirstOfMonth)
     AND Claim_Registered_Date < @FirstOfMonth
		THEN "02 - 1 to 2 Months"

WHEN overall_stat = "Outstanding"
     AND Claim_Registered_Date >= DATEADD(mm, -6, @FirstOfMonth)
     AND Claim_Registered_Date < DATEADD(mm, -2, @FirstOfMonth)
		THEN "03 - 2 to 6 Months"