Hello superchew,

Add this macro to the ThisWorkbook module of your VBA Project. The calendar will pop up on all worksheets fro cells F22 and H22.

Change "UserForm1" to the name of your calendar.
Private Sub Workbook_SheetChange(ByVal Sh As Object, ByVal Target As Range)
    If Target.Address = "$F$22" Or Target.Address = "$H$22" Then
        UserForm1.Show
    End If
End Sub