Microsoft KB Archive/81694

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XL: Formula to Calculate Number of Days in Month

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The information in this article applies to:


 * Microsoft Excel for Windows, versions 3.0, 4.0, 4.0a, 5.0, 5.0c
 * Microsoft Excel for OS/2
 * Microsoft Excel for the Macintosh, versions 3.0, 4.0, 5.0, 5.0a
 * Microsoft Excel for Windows, versions 7.0, 7.0a
 * Microsoft Excel 97 for Windows
 * Microsoft Excel 98 Macintosh Edition

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SUMMARY
In Microsoft Excel, you can use the 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

  =DAY(DATE(YEAR(The_Date),MONTH(The_Date)+1,0))

where The_Date is the starting date.

This formula works by finding the &quot;zeroth&quot; day of the month after The_Date. Because there is no &quot;zeroth&quot; 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

  =DAY(DATE(my_year,my_month+1,1)-1)

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 Excel Versions 5.0 and Later
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http://www.microsoft.com/support/supportnet/overview/overview.asp

In Microsoft Excel versions 5.0 and later, 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