property Calendar.ShowNonMonthDays as Boolean
Specifies whether the calendar panel displays the dates that are not part of the month.

TypeDescription
Boolean A boolean expression that specifies whether dates that belongs to another months are displayed on the calendar panel.  
By default, the ShowNonMonthDays property is True. You can use the ShowNonMonthDays property to hide dates that are not belonging to the browsing month.

The following screen shot shows May 2012, while 29, 30 are from April, and 1 - 9 from June, non month days, ( ShowNonMonthDays is True, by default ):

The following screen shot shows only May 2012, ( ShowNonMonthDays is False ):