As you already know Christmas Day falls on Monday, December 25th this year.  Christmas is a Holy Day of Obligation.  There has been a lot of confusion is some circles about Mass.  So let me try to help out.  The first thing to remember is even with the Holy Day falling on Monday you still have your Sunday Obligation.

So with that in mind here goes.

On Saturday December 23rd there is a Vigil Mass for Sunday at 5PM.  This fulfills your Sunday Obligation only

On Sunday December 24th we have our normally scheduled Masses at 9:00 AM and 11:30 AM.  These Masses fulfill your Sunday Obligation Only, not your Christmas Obligation.

On Sunday December 24th we have also have two Christmas Eve Masses:

The 4:30 PM Children’s Christmas Eve Mass and the 9:00 PM Christmas Eve Mass.

Attending either of these two Masses fulfills your CHRISTMAS OBLIGATION ONLY.  Even though they occur on Sunday they do not fulfill your Sunday Obligation.

So is it possible you may go to mass twice on Sunday to fulfill both your Sunday Obligation and your Holy Day Obligation?  YES.

There is also the Mass of Christmas Day at 9:00 AM on December 25th and this of course fulfills your Christmas Day Obligation.

Hope this helps