First and Last Day of Month User Defined Functions

I often find myself in a situation where I need to return the first or last day of the month in various queries. Despite this being a seemingly simple process (that I'm sure EVERYONE needs at some point), Microsoft's method of obtaining this data is pointlessly cumbersome. The following piece of code will return the last day of today's month

SELECT DATEADD(ms, -3, DATEADD(mm, DATEDIFF(m, 0, GETDATE())+1, 0))

To me, this is simply ridiculous. First of all, there's so many nested functions in this query that I can't keep them all straight. Next, there's NO way you can remember it all to plug in to a query at any given moment (was this a +1 or a -1 at this spot??). So, below is some code to create two user defined functions that will return either the first day of the month or the last day of the month of any given date passed to the function.

First Day of Month:

USE [son_db]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION [dbo].[udfFirstDayOfMonth]
(
@startDate DATETIME
)
RETURNS DATETIME
AS
BEGIN

RETURN DATEADD(mm, DATEDIFF(mm,0,@startDate), 0)

END

Last Day of Month:

USE [son_db]
GO

SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO

CREATE FUNCTION [dbo].[udfLastDayOfMonth]
(
@startDate DATETIME
)
RETURNS DATETIME
AS
BEGIN

RETURN DATEADD(ms,-3,DATEADD(mm, DATEDIFF(m,0,@startDate)+1, 0))

END

To use the user defined functions, simply pass a date to the function as a variable in your SELECT statement.

SELECT dbo.udfFirstDayOfMonth(GETDATE()) --First date of this month
SELECT dbo.udfFirstDayOfMonth(GETDATE()-5) --First date of the month 5 days prior to today

This should make using beginning and ending dates of months a bit easier for you.