XL: Formula to Calculate Number of Days in Month

• Microsoft Excel for Windows, versions 3.0, 4.0, 4.0a, 5.0, 5.0c
• Microsoft Excel for OS/2, versions 2.20, 2.21, 3.0
• Microsoft Excel for the Macintosh, versions 3.0, 4.0, 5.0, 5.0a
• Microsoft Excel for Windows 95, versions 7.0, 7.0a
• Microsoft Excel 97 for Windows
• Microsoft Excel 98 Macintosh Edition

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))

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

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

MORE INFORMATION

Microsoft Excel Versions 5.0 and Later

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   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

REFERENCES

"Function Reference" version 3.0, pages 44, 46, 156, 251