This year, Christmas is on a Sunday.
Am little confused. On my calender, in the United States, December 25 falls on a Monday. One has an obligation to fulfill the Sunday obligation, and the obligation of the Holy Day, The Nativity of Christ (Christmas) on Monday the 25. As others have said, no two-fors.
One other thing. To meet your Lord, your Creator, your Redeemer at the memorial of His Sacrifice of His eternal Love for you (the Mass) is an obligation?? I’ve come to find that word (in a certain way) offensive. I would think the term opportunity, (as in another opportunity to receive Christ) would be more appropriate. Though I am sure it will never happen, I would love to see the church change the term to Holy Day of Opportunity. I am certain that for many, in our old age, due to infirmity of many kinds, we will wish for the days we have the opportunity (and the ability) to attend Mass and long for the ability to fulfill the 'obligation" to sit with our Lord.
My two cents.