How do I get the old value of a changed cell in Excel VBA?

try this

declare a variable say

Dim oval

and in the SelectionChange Event

Public Sub Worksheet_SelectionChange(ByVal Target As Range)
oval = Target.Value
End Sub

and in your Worksheet_Change event set

old_value = oval

You can use an event on the cell change to fire a macro that does the following:

vNew = Range("cellChanged").value
Application.EnableEvents = False
Application.Undo
vOld = Range("cellChanged").value
Range("cellChanged").value = vNew
Application.EnableEvents = True 

I had to do it too. I found the solution from "Chris R" really good, but thought it could be more compatible in not adding any references. Chris, you talked about using Collection. So here is another solution using Collection. And it's not that slow, in my case. Also, with this solution, in adding the event "_SelectionChange", it's always working (no need of workbook_open).

Dim OldValues As New Collection

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
    'Copy old values
    Set OldValues = Nothing
    Dim c As Range
    For Each c In Target
        OldValues.Add c.Value, c.Address
    Next c
End Sub

Private Sub Worksheet_Change(ByVal Target As Range)
    On Local Error Resume Next  ' To avoid error if the old value of the cell address you're looking for has not been copied
    Dim c As Range
    For Each c In Target
        Debug.Print "New value of " & c.Address & " is " & c.Value & "; old value was " & OldValues(c.Address)
    Next c
    'Copy old values (in case you made any changes in previous lines of code)
    Set OldValues = Nothing
    For Each c In Target
        OldValues.Add c.Value, c.Address
    Next c
End Sub