Answer:
If you're thinking Christmas '13 is a Thursday because Christmas '11 was a Sunday and Christmas '12 is a Tuesday, normally each date on the calendar falls on the next weekday in the next year, but it skips a day when there's a February 29 (leap year day) in between the two dates. So Christmas '13 is a Wednesday, Christmas '14 is a Thursday, Christmas '15 is a Friday, and, since 2016 is a leap year, Christmas '16 is a Sunday.