Example
'if only one area (not multiple areas):
With Range("A3:D20")
Debug.Print .Cells(.Cells.CountLarge).Row
Debug.Print .Item(.Cells.CountLarge).Row 'using .item is also possible
End With 'Debug prints: 20
'with multiple areas (also works if only one area):
Dim rngArea As Range, LastRow As Long
With Range("A3:D20, E5:I50, H20:R35")
For Each rngArea In .Areas
If rngArea(rngArea.Cells.CountLarge).Row > LastRow Then
LastRow = rngArea(rngArea.Cells.CountLarge).Row
End If
Next
Debug.Print LastRow 'Debug prints: 50
End With