SQL Server Convert UTC to EST/EDT (Eastern Daylight Time)

fn_utc_to_edt.sql

/*** fn_utc_to_edt ***/
IF NOT EXISTS (SELECT   1
               FROM     [INFORMATION_SCHEMA].[ROUTINES]
               WHERE    [ROUTINE_NAME] = 'fn_utc_to_edt'
                        AND [ROUTINE_TYPE] = 'FUNCTION')
  BEGIN
   EXEC('CREATE FUNCTION [dbo].[fn_utc_to_edt]() RETURNS INT AS BEGIN RETURN 1 END')
  END;
GO

ALTER FUNCTION [dbo].[fn_utc_to_edt] (@utc DATETIME)
  RETURNS DATETIME
  AS
    BEGIN
      -- Convert UTC to EST accouting for EDT/DST
      DECLARE @edt DATETIME;

      SET @edt = DATEADD(
        hh, 
        CASE
          WHEN YEAR(@utc) <= 2006 THEN 
            CASE
              WHEN @utc >= '4/' + CAST((8 - DATEPART(dw, '4/1/' + CAST(YEAR(@utc) AS VARCHAR))) % 7 + 1 AS VARCHAR) + '/' + CAST(YEAR(@utc) AS VARCHAR) + ' 7:00'
                AND @utc < '10/' + CAST(32 - DATEPART(dw, '10/31/' + CAST(YEAR(@utc) AS VARCHAR)) AS VARCHAR) + '/' + CAST(YEAR(@utc) AS VARCHAR) + ' 6:00' 
                THEN -4
              ELSE -5
            END
          ELSE 
            CASE
              WHEN @utc >= '3/' + CAST((8 - DATEPART(dw, '3/1/' + CAST(YEAR(@utc) AS VARCHAR))) % 7 + 8 AS VARCHAR) + '/' + CAST(YEAR(@utc) AS VARCHAR) + ' 7:00'
                  AND @utc < '11/' + CAST((8 - DATEPART(dw, '11/1/' + CAST(YEAR(@utc) AS VARCHAR))) % 7 + 1 AS VARCHAR) + '/' + CAST(YEAR(@utc) AS VARCHAR) + ' 6:00' 
                  THEN -4
              ELSE -5
            END
        END, 
        @utc);

      RETURN @edt;
    END;