doing quarterly arithmetic instead of monthly

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SQL-Server-2008R2

Dear Expert,

I have the following which does month arithmetic as follows in ms sql server stored procedure.

@CCMTH is the current month
@CCYR is the current year all in an incremental loop

IF @CCMTH = 12
BEGIN	
SET @CCMTH = 1	
SET @CCYR = @CCYR+1
END
ELSE
IF @CCMTH <> 12	
BEGIN
SET @CCMTH =@CCMTH+1	
SET @CCYR =@CCYR
END

Need to apply the same concept now on quarterly basics i.e the increment will now be 3 instead of 1.

Please provide the codes to cater for this.
The challenge is how to handle when the increment in month goes beyond 12

Thanks