I've managed to work out the code need (I think)

BUT

I need to know how I attach it to a cell. I need the code to look at the cell and decide whether or not to display the message box.

I'm not sure if the "Range(E5)" is the correct way of doing this.

Sub Over50()
Dim WeekNumber As Integer
WeekNumber = Range(E5)
If WeekNumber > 50 Then
MsgBox "To Many Weeks. This Number Will remain 50"
End If

End Sub