vbscript custom excel function

Function HoldayTaken(Employee As String, StartDate As Date, EndDate As Date) As Integer
    Application.Volatile True
    Dim ExclDates
    'We Grab the year from our records to keep it current
    NewYearDay = "01/01"
    Christmas = "25/12"

    Dim tbl As ListObject
    Set tbl = Sheets("DataSheet").ListObjects("Holidays")
    Dim Enabled_ As Boolean
    Enabled_ = True
    With tbl
        For i = 1 To .ListRows.Count
            If .DataBodyRange(i, 1).Value = Employee Then
                'If Holday StartDate is within Range
                If .DataBodyRange(i, 2).Value >= StartDate And .DataBodyRange(i, 2).Value <= EndDate Then
                    'If Holiday EndDate is within Range
                    If .DataBodyRange(i, 3).Value >= StartDate And .DataBodyRange(i, 3).Value <= EndDate Then
                        'Return Days
                        Tally = Tally + DateDiff("d", .DataBodyRange(i, 2).Value, .DataBodyRange(i, 3).Value)
                    'If Holiday EndDate is out of range
                    ElseIf .DataBodyRange(i, 3).Value >= EndDate Then
                        Tally = Tally + DateDiff("d", .DataBodyRange(i, 2).Value, EndDate)
                    End If

                    'Apply 1 to date
                    If Enabled_ Then
                        Tally = Tally + 1
                        Enabled_ = False
                    End If

                'If Holiday covers the entire week
                ElseIf .DataBodyRange(i, 3).Value < StartDate And .DataBodyRange(i, 3).Value > EndDate Then
                    Tally = Tally + DateDiff("d", StartDate, EndDate)

                    'Apply 1 to date
                    If Enabled_ Then
                        Tally = Tally + 1
                        Enabled_ = False
                    End If

                'If Holiday StartDate is less than Week StartDate
                ElseIf .DataBodyRange(i, 2).Value < StartDate Then
                    If .DataBodyRange(i, 3).Value >= StartDate And .DataBodyRange(i, 3).Value <= EndDate Then
                        Tally = Tally + DateDiff("d", StartDate, .DataBodyRange(i, 3).Value)

                        'Apply 1 to date
                        If Enabled_ Then
                            Tally = Tally + 1
                            Enabled_ = False
                        End If

                    Else
                        Tally = Tally + 0
                    End If
                Else
                    Tally = Tally + 0
                End If

                If DateValue(Christmas & "/" & Year(.DataBodyRange(i, 2).Value)) >= StartDate And DateValue(Christmas & "/" & Year(.DataBodyRange(i, 2).Value)) <= EndDate Then
                    If DateValue(Christmas & "/" & Year(.DataBodyRange(i, 2).Value)) >= .DataBodyRange(i, 2).Value And DateValue(Christmas & "/" & Year(.DataBodyRange(i, 3).Value)) <= .DataBodyRange(i, 2).Value Then
                        Tally = Tally - 1
                    End If
                ElseIf DateValue(Christmas & "/" & Year(.DataBodyRange(i, 3).Value)) >= StartDate And DateValue(Christmas & "/" & Year(.DataBodyRange(i, 3).Value)) <= EndDate Then
                    If DateValue(Christmas & "/" & Year(.DataBodyRange(i, 3).Value)) >= .DataBodyRange(i, 2).Value And DateValue(Christmas & "/" & Year(.DataBodyRange(i, 3).Value)) <= .DataBodyRange(i, 3).Value Then
                        Tally = Tally - 1
                    End If
                End If

                If DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 2).Value)) >= StartDate And DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 2).Value)) <= EndDate Then
                    If DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 2).Value)) >= .DataBodyRange(i, 2).Value And DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 2).Value)) <= .DataBodyRange(i, 3).Value Then
                        Tally = Tally - 1
                    End If
                ElseIf DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 3).Value)) >= StartDate And DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 3).Value)) <= EndDate Then
                    If DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 3).Value)) >= .DataBodyRange(i, 2).Value And DateValue(NewYearDay & "/" & Year(.DataBodyRange(i, 3).Value)) <= .DataBodyRange(i, 3).Value Then
                        Tally = Tally - 1
                    End If
                End If

            End If
        Next i
    End With

    HoldayTaken = Tally

End Function