XL: How to Calculate the Number of Days in a Month

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In Microsoft Excel, you can use date functions to calculate the number of days in a month. For example, you can use the following formula to return the number of days in a month, based on a given starting date
where The_Date is the starting date.

This formula works by finding the "zeroth" day of the month after The_Date. Because there is no "zeroth" day of any month, this date is interpreted as the last day of the month containing The_Date. The DAY function then converts this date into a day number.

Or, to calculate the number of days in a month, given the month and year, use the following function
where my_month is the month for which you want to return the number of days, and my_year is the year. This function calculates the first day of the next month and subtracts 1, which equals the last day of the current month. The DAY function then gives you the day of the month.


Microsoft provides programming examples for illustration only, without warranty either expressed or implied, including, but not limited to, the implied warranties of merchantability and/or fitness for a particular purpose. This article assumes that you are familiar with the programming language being demonstrated and the tools used to create and debug procedures. Microsoft support professionals can help explain the functionality of a particular procedure, but they will not modify these examples to provide added functionality or construct procedures to meet your specific needs.
If you have limited programming experience, you may want to contact a Microsoft Certified Partner or Microsoft Advisory Services. For more information, visit these Microsoft Web sites:

Microsoft Certified Partners - https://partner.microsoft.com/global/30000104

Microsoft Advisory Services - http://support.microsoft.com/gp/advisoryservice

For more information about the support options that are available and about how to contact Microsoft, visit the following Microsoft Web site:http://support.microsoft.com/default.aspx?scid=fh;EN-US;CNTACTMS In Microsoft Excel, you can also use the following Visual Basic for Applications procedure:
Sub Test()
    Dim m As Integer, y As Integer, DaysInMonth As Integer
    ' define variable for number of the month, in this example, November
    m = 11
    ' define variable for the year
    y = 1994
    DaysInMonth = DateSerial(y, m + 1, 1) - DateSerial(y, m, 1)
    MsgBox DaysInMonth
End Sub


For more information about functions, click Microsoft Excel Help on the Help menu, type about using functions to calculate values in the Office Assistant or the Answer Wizard, and then click Search to view the topics returned.


Article ID: 214313 - Last Review: January 24, 2007 - Revision: 2.4
  • Microsoft Excel 2000 Standard Edition
  • Microsoft Excel 2002 Standard Edition
  • Microsoft Excel 97 Standard Edition
  • Microsoft Excel 2001 for Mac
  • Microsoft Excel 98 for Macintosh
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