Excel – Show date format in Excel as the OS default

1) Exit Excel 2007.
2) Start Registry Editor.
3) Locate and then click the following registry subkey:

HKEY_CURRENT_USER\Software\Microsoft\Office\12.0\Excel\Security

4) On the Edit menu, point to New, and then click DWORD Value.
5) Type ExtensionHardening, and then press ENTER.
6) Right-click ExtensionHardening, and then click Modify.
7) In the Value data box, type 0, and then click OK.

The following list contains the value data settings that are appropriate for the ExtensionHardening setting:

0: Do not check the file name extension and the file type, and bypass the function of the warning message.
1: Check the file name extension and the file type. If they do not match, display the warning message.
2: Check the file name extension and the file type. If they do not match, do not open the file.

Note: The default value data is 1. When the value data is set to 1, the behavior becomes the same as when no registry value is set. When the value data is set to 0, the file name extension and the file content are not checked in all situations. It is not recommended bypassing this function.

8) On the File menu, click Exit to exit Registry Editor.

I tried it with 30/01/2010

SUBSTITUTE(A1,".","/")

and then I put in

=TEXT(B1, "yyyy-mm-dd").

The result was expected.

I suspect the issue is the cell you are doing this too is not in date format.

For example, if I change my value to 30.01.2010 then the value is then duplicated (in the same manner you describe)

Or, you could keep it as

=TEXT(A1, "yyyy-mm-dd")

And update all the . to / with a quick macro

Option Explicit
Sub ReplaceDate()

Dim row As Integer
row = 1

Do While (Range("A" & row).Value <> "")

    Dim val As String
    val = Range("A" & row).Value

    Dim i As Integer

    Dim result As String
    result = ""

    Dim spl() As String
    spl = Split(val, ".")

    If (UBound(spl) > 0) Then


    For i = 0 To Len(val)

    Dim r As String
        result = result & Replace(Mid(val, i + 1, 1), ".", "/")
    Next i

    End If

    If result <> "" Then

        Range("A" & row).NumberFormat = "@"
        Range("A" & row).Value = result

    End If

row = row + 1
Loop

End Sub

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