Use the CalendarHandle property to get the calendar control's window handle. 

The CalendarHandle property is declared but not implemented in TCommonCalendar. 

For descendants that use only one window, such as TMonthCalendar, CalendarHandle is the same as the Handle property. However, some TCommonCalendar descendants such as TDateTimePicker are implemented using more than one window. In these classes, CalendarHandle is the window handle for the portion of the control that displays date values. 

Handle