From The Texas Catholic
While there may be two-for-one specials for Christmas shopping, there are none for the obligations to attend Mass on Christmas.
This year, the Fourth Sunday of Advent falls on the same day as Christmas Eve (Dec. 24), with Christmas falling on Monday, Dec. 25. In this case, there are two distinct obligations to attend Mass: the Sunday obligation and the Christmas obligation. No single Mass fulfills both a Catholic’s Sunday obligation and the Christmas obligation. Because they are different liturgical days — even if they overlap on the calendar — they require attendance at different Masses.
The Sunday obligation may be fulfilled by attending Mass after 4 p.m. on Saturday, Dec. 23, or by attending Mass at any time on Sunday, Dec. 24. The Christmas obligation may be fulfilled by attending Mass after 4 p.m. on Sunday, Dec. 24, or by attending Mass at any time on Christmas, Dec. 25.
Regardless of when Catholics attend Mass, though, they must attend two separate Masses to fulfill both obligations.
