Calculate First day of given date

SQL Server 2012 is having in-bulit EOMONTH() date function to get the end of month;

The below is the query to get first day of month...

DECLARE @Date datetime = '2015-01-28'
SELECT @Date GivenDate, DATEADD(mm,DATEDIFF(mm,0,@Date),0) FirstDayOfGivenMonth

OutPut:

GivenDate 	         FirstDayOfGivenMonth  
2015-01-28 00:00:00.000	 2015-01-01 00:00:00.000