mass?

What happens when Christmas day falls on a Sat. or Mon.?

Then we are still obligated to go both on Christmas Day and Sunday.

usccb.org/beliefs-and-teachings/what-we-believe/canon-law/complementary-norms/canon-1246.cfm

I presume you are asking about what happens to the feast day/celebration of the Mass.

The answer is “nothing”.

The Feast of the Nativity (a.k.a. Christmas) is never transferred or abrogated. Therefore, Dec 25 would be a holy day of obligation no matter what day it falls on.

The Sunday immediately before or after would also be a holy day of obligation in the case when Christmas is on a Saturday or Monday.

I thought so, but I couldn’t remember the last time Christmas fell on a Sat or Mon, what I did.

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