XL: IsDate Function Incorrectly Identifies Some Expressions

ID: Q184521

The information in this article applies to:

SYMPTOMS

In the programs that are listed at the beginning of this article, if you run a Visual Basic for Applications macro that uses the IsDate function to determine whether an expression can be converted into a date, the function may return the Boolean value True. This result is incorrect.

CAUSE

This problem occurs if the expression that is being evaluated by the IsDate function uses a date format that is not normally recognized as valid by Microsoft Excel. The following date formats are not recognized. 

   Format           Example
   -----------------------------

   year-day-month   2002, 5 July
   month-year-day   July, 2002 5
   day-year-month   5, 2002 July
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   http://www.microsoft.com/support/supportnet/refguide/
For example, if you run the following macro 

   Sub TestIsDateFunction()
       MyDate = "2002, 5 July"   'an invalid date expression
       MsgBox IsDate(MyDate)     'is it a date?
   End Sub
the message box displays True instead of False even though the date is not valid in Microsoft Excel.

RESOLUTION

If an expression uses a date format that includes a year, a month, and a day, in any order, the IsDate function returns True. There is no way to prevent this behavior.

However, you can use the CDate function to convert invalid expressions into valid dates, for example: 

   Sub ConvertDate()
       MyDate = "2002, 5 July"   'an invalid date expression
       CnDate = CDate(MyDate)    'convert MyDate into a valid date
       MsgBox CnDate             'display the new, valid date
   End Sub

STATUS

This behavior is by design of Visual Basic for Applications.

MORE INFORMATION

Depending on the regional settings that are in use on your computer, Microsoft Excel normally recognizes expressions that use any of the following formats as dates. 

   Format           Example
   -----------------------------

   month-day-year   July 5, 2002
   day-month-year   5 July, 2002
   year-month-day   2002, July 5
For example, if you enter "July 5, 2002" into a cell, Microsoft Excel converts this expression into a proper date.

Expressions that use other formats (such as year-day-month) are not recognized as dates by Microsoft Excel. However, because of the design of the IsDate function, it returns True for any expression that contains a year, a month, and a day, in any order.

Additional query words: XL97 XL5 XL7 5.0 7.0 year2000 y2k year 2000 

Keywords          : kbprg kbdta kbdtacode OffVBA xlformula KbVBA 
Version           : MACINTOSH:5.0,5.0a; WINDOWS:5.0,5.0c,7.0,7.0a,97
Platform          : MACINTOSH WINDOWS
Issue type        : kbprb

Last Reviewed: May 18, 1999