Excel VB count the number of weeks between two cells - vba

Question

Hello everybody peeps,
I'm extremely new to VB and I've been taking bits of code of the web trying to create something quite simple. I'm trying to get excel to calculate the number of weeks between two cells with date values. The first cell is in a fixed location, the second cell is the last cell within that columns used range.
Last is a function I pinched off the web. I can't get this to work at all, any help would be much appreciated.
Sub test_date_calc()
Dim LastCell As String
Dim nwks As Integer
Dim rng As Range
Set rng = Sheets("data13").UsedRange
LastCell = Last(3, rng)
nwks = (Cells(3, 2) - LastCell.Value) / 7
If nwks > 13 Then
MsgBox "greater"
Else
MsgBox "Less"
End If
End Sub
the Last function below, which may help
Function Last(choice As Long, rng As Range)
'Ron de Bruin, 5 May 2008
' 1 = last row
' 2 = last column
' 3 = last cell
Dim lrw As Long
Dim lcol As Long
Select Case choice
Case 1:
On Error Resume Next
Last = rng.Find(What:="*", _
After:=rng.Cells(1), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByRows, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Row
On Error GoTo 0
Case 2:
On Error Resume Next
Last = rng.Find(What:="*", _
After:=rng.Cells(1), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByColumns, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Column
On Error GoTo 0
Case 3:
On Error Resume Next
lrw = rng.Find(What:="*", _
After:=rng.Cells(1), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByRows, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Row
On Error GoTo 0
On Error Resume Next
lcol = rng.Find(What:="*", _
After:=rng.Cells(1), _
Lookat:=xlPart, _
LookIn:=xlFormulas, _
SearchOrder:=xlByColumns, _
SearchDirection:=xlPrevious, _
MatchCase:=False).Column
On Error GoTo 0
On Error Resume Next
Last = rng.Parent.Cells(lrw, lcol).Address(False, False)
If Err.Number > 0 Then
Last = rng.Cells(1).Address(False, False)
Err.Clear
End If
On Error GoTo 0
End Select
End Function

Answer 1

I think your error is due to this line:
nwks = (Cells(3, 2) - LastCell.Value) / 7
LastCell is a string so it doesn't need the .Value
nwks = (Cells(3, 2) - LastCell) / 7
You can use the DATEDIFF function in VBA.
DateDiff( interval, date1, date2, [firstdayofweek], [firstweekofyear] )
Usage example:
nwks = DateDiff("ww", Cells(3, 2).Value, LastCell.Value)
You can see the documentation for DATEDIFF HERE