# SQL SERVER – UDF – User Defined Function – Get Number of Days in Month

Following User Defined Function (UDF) returns the numbers of days in month. It is very simple yet very powerful and full proof UDF.
`CREATE FUNCTION [dbo].[udf_GetNumDaysInMonth] ( @myDateTime DATETIME ) RETURNS INT AS BEGIN DECLARE @rtDate INT SET @rtDate = CASE WHEN MONTH(@myDateTime) IN (1, 3, 5, 7, 8, 10, 12) THEN 31 WHEN MONTH(@myDateTime) IN (4, 6, 9, 11) THEN 30 ELSE CASE WHEN (YEAR(@myDateTime) % 4 = 0 AND YEAR(@myDateTime) % 100 != 0) OR (YEAR(@myDateTime) % 400 = 0) THEN 29 ELSE 28 END END RETURN @rtDate END GO `
Run following script in Query Editor:
`SELECT dbo.udf_GetNumDaysInMonth(GETDATE()) NumDaysInMonth GO `
ResultSet:
NumDaysInMonth
———————–
31

Reference : Pinal Dave (https://blog.sqlauthority.com)

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• Thanks Simon,

I have used similar logic many times. I just decided to do something different. You can check other datetime related articles here.

https://blog.sqlauthority.com/tag/sql-datetime/

Regards,
Pinal Dave ( https://blog.sqlauthority.com/ )

• You really don’t need to do the math, you can just get the last day of the month using built in date functions and assign that to your return variable. This is built in for you so you don’t have to worry about leap years or anything

CREATE FUNCTION [dbo].[udf_GetNumDaysInMonth] ( @myDateTime DATETIME )
RETURNS INT
AS
BEGIN
DECLARE @rtDate INT
RETURN @rtDate
END
GO

• Hello, Expert

I’m using Transact-Query, how I select a particular month out of in different years in the database?

The format column field 2005/08/26…….

thanks you
ryan,

September 17, 2007 3:49 am

Hi This User defined function will return the no. of days in a month

CREATE FUNCTION [dbo].[ufn_GetDaysInMonth](
@CurrentDate DATETIME )
RETURNS INT
AS
BEGIN
DECLARE @ReturnDays INT
SET @ReturnDays =
CASE WHEN MONTH(@CurrentDate) IN (1, 3, 5, 7, 8, 10, 12) THEN 31
WHEN MONTH(@CurrentDate) IN (4, 6, 9, 11) THEN 30
ELSE
CASE WHEN (YEAR(@CurrentDate) % 4 = 0 AND YEAR(@CurrentDate) % 100 != 0) OR (YEAR(@CurrentDate) % 400 = 0) THEN 29
ELSE 28
END
END
RETURN @ReturnDays
END

–SELECT dbo.ufn_GetDaysInMonth(GETDATE()) No_Of_Days_In_Month
GO

• Try this one-liner:
CREATE FUNCTION [dbo].[ufn_GetDaysInMonth](
@CurrentDate DATETIME )
RETURNS INT
AS
BEGIN
END

• Hi pinaldave,

Thank you very much

• Just a modification to Doug’s posting :

CREATE FUNCTION [dbo].[ufn_GetDaysInMonth] (@CurrentDate DATETIME )
RETURNS INT
AS
BEGIN
DECLARE @RetDate INT
RETURN @RetDate
END

— SELECT [dbo].[ufn_GetDaysInMonth] (‘2008/02/25’)

• EXCELLENT …:))

EXACTLY SUITS MY REQUIREMENT

SUPERB

THNX A LOT………

• Mahesh K Rajan
October 13, 2008 2:09 pm

We have already some built in functions avail, then why should we go behind all those steps…
Anyway, good logic…
-Mahesh

• I want No.of days in a Month – Here i will give Month(2) and Year(2009),

so, there are two parameters.

Pls Give me the function

• There are many ways

Here is one

declare @month int, @year int
select @month=2, @year=2009

• hi.. experts… i need a similar UDF…
my req is…. if i give 3 param’s to the UDF.. like..
“month,year and dayofweek” then i should get a list of that day fom the given month,year

ex. for April 2009 Sunday
UDFDays(@mm,@yy,@dyw)
i.e UDFDays(04,2009,’Sunday’)
then i should get list as..

6
13
20
27

i.e… the dates from the month given for weekday.. like for Apil 2009 Saturday..
i expect..esult as

5
12
19
26

etc…

• Re post:… slight mistake frm my side…

hi.. experts… i need a similar UDF…
my req is…. if i give 3 param’s to the UDF.. like..
“month,year and dayofweek” then i should get a list of that day fom the given month,year

ex. for April 2009 Sunday
UDFDays(@mm,@yy,@dyw)
i.e UDFDays(04,2009,’Sunday’)
then i should get list as..

5
12
19
26
i.e… the dates from the month given for weekday.. like for Apil 2009 Saturday..
i expect..esult as

4
11
18
25

etc…

• @gourav, here’s a quick shot:
CREATE FUNCTION UDFDays(@mm tinyint,@yy smallint,@dyw varchar(9))
RETURNS TABLE
AS
RETURN
WITH
Data(The_Date)
AS
(
SELECT CONVERT(smalldatetime, CAST(@mm as varchar(2)) + ‘/01/’ + CAST(@YY as varchar(4)) , 101)
),
Days_In_Month
AS
(
UNION ALL
SELECT DATEADD(d, 1, The_Date), Next_Month FROM Days_In_Month WHERE The_Date < Next_Month
)
SELECT
DATEPART(d, The_Date) Day_Number
FROM
Days_In_Month
WHERE
DATENAME(dw, The_Date) = @dyw;
GO

• thanks bro… you hav done it….thank you very very much…
Regards
Gourav

• Very Informative site….

• Mrityunjay Ravi
February 26, 2010 2:47 pm

Hi expert,

You are excelent to write this function.

Thank you very much………………..

• We can write this also instead of case when if someone feels difficulty in using case statements then it will be easy for them using this…………………..
create function dbo.retdates(@date datetime)
returns int
as
begin
declare @out int
if month (@date) in(1,3,5,7,8,10,12)
set @out=31
else if month(@date) in(4,6,9,11)
set @out=30
else if ((year(@date)%4=0) and (year(@date)%100!=0)) or (year(@date)%400=0)
set @out=29
else
set @out=28
return @out
end
go

• I want to subscribe

• How do i find number of sundays in given month?

• Hi,

what are the major difference between functions and Procedures?

• Imran Mohammed
July 22, 2010 6:03 am

@Pavan.

Major Difference between Function and Procedure.

Function should return a value where as procedure might or might not.

You cannot run select statement on procedures where as you can run a select statement on (Table) functions.

You cannot perform many T-SQL operation inside a function where as you perform many more T-SQL Operations inside a procedure.

~Peace.

• Hello Friends,
This site was very informative, i have an issue, would be glad if you can help me.
The issue that i have to write a user defined funtion

format of dtActivityStartDate/dtActivityFinishDate: 2010-09-17 14:50:51.150 Note: Both dtActivityStartDate/dtActivityFinishDate

vcActivityName = Process Request

usdFuncTimeCalc (vcActivityName,dtActivityStartDate, dtActivityFinishDate)

i need to calculate time elasped for that type of activity following are the rules:

(If Process Request is the activity)

Working Days: Monday through Saturday
Hours of Operation: 9AM – 5PM

only working hours of day need to the counted like for example if it is sep 15 11 Am is dtActivityStartDate & Sep 17 is dtActivityFinishDate is 10 Am. then time elapsed is 11am to 5pm on sep 15 , 9 to 5 on sep 16 & 9 to 10 on sep 17 so total should be
6+ 8 + 1 = 15 hours + minutes.

format of date time: 2010-09-17 14:50:51.150

vcActivityName = Process Request