Calculate Number of Working Days in SQL Server

I recently bumped into this handy query from CMS which shows how to calculate the number of working days in this year till now. The working days are assumed to be Monday to Friday and does not include public holidays, which may be added by you later depending on the country you live in.

DECLARE @StartDate DATETIME

DECLARE @EndDate DATETIME

SET @StartDate = '2009/1/01'

SET @EndDate = GETDATE()

SELECT  

(DATEDIFF(dd, @StartDate, @EndDate) + 1)

-(DATEDIFF(wk, @StartDate, @EndDate) * 2) 

-(CASE WHEN DATENAME(dw, @StartDate) = 'Sunday' THEN 1 ELSE 0 END)

-(CASE WHEN DATENAME(dw, @EndDate) = 'Saturday' THEN 1 ELSE 0 END)

Assuming the current date is 'May 20, 2009', the number of working days after this query is 100