Whatever format is in the Windows Regional and Language Settings governs what
the format is in the header or footer.
These are very limited and Excel recognizes only a few for header formatting.
To get a header date format of your choosing use a cell reference for the
header.
e.g. In A1 enter =TEXT(DATE(2006,12,10),"dddd, mmmm d"&", "&"yyyy")
Then run this macro.
Sub CellInHeader()
With ActiveSheet
..PageSetup.CenterHeader = Range("A1").Value
End With
End Sub
Gord Dibben MS Excel MVP