This year, the Solemnity of Mary, the Holy Mother of God (January 1 – New Year’s Day) is on a Monday, so it is not a Holy Day of Obligation. It remains a Holy Day, however, attending Mass on this day is not required.
The Nativity of the Lord (commonly called Christmas) also falls on a Monday this year, however, it remains a Holy Day of Obligation. Catholics are required to attend Mass on either Saturday, December 23 or Sunday, December 24 for the Fourth Sunday of Advent. And, they must also attend either the Christmas Eve (Vigil Mass) or Mass on Christmas Day to meet the Christmas obligation.