Christmas has twelve days,as we all surely know from the song. (So "Kwanza" would be the Second to Eighth day of Christmas). The Epiphany on 6th January is the last day of Christmas, in the Western tradition. Or in the Orthodox tradition, the 6th is the first day of Christmas. Or "Old Christmas Day", as it is sometimes called.

Noone has ever seriously suggested that Christmas Day is supposed to be Jesus's actual birthday, it's just a day picked to celebrate it, at a time of the year when a celebration is needed, and is generally held in most Northern Hemisphere cultures. (And to match up with it March 25th was picked to celebrate the Annunciation.)

I always think it's rough on people in the Southern hemisphere, having Christmas in the middle of summer, and no equivalent feast in the middle of winter, so far as I am aware.