ufnAddBusinessDays SqlServer function

ufnAddBusinessDays.sql

CREATE FUNCTION [dbo].[ufnAddBusinessDays]
(
	@Date DATE,
	@n int -- Number of days to add or substract
)
RETURNS DATE
AS
BEGIN
	DECLARE @d INT,@f INT,@DW INT;
	Set @f = CAST(abs(1^SIGN(DATEPART(DW, @Date)-(7-@@DATEFIRST))) as bit)
	Set @DW =  DATEPART(DW,@Date)-(7-@@DATEFIRST)*(@f^1)+@@DATEFIRST*(@f&1) --Calculate the Day of the Week regardless the @@DATEFIRST configuration
	SET @d=4-SIGN(@n)*(4-@DW);
	RETURN DATEADD(D,@n+((ABS(@n)+(@d%(8+SIGN(@n)))-2)/5)*2*SIGN(@n)-@d/7,@Date);
END

Based on this SO answer.

Features

• No loops
• No tables,
• No case statements
• No DATEFIRST dependency
• Works with negatives