This is a question which comes up each year. It came up again today.
Must we do penance on Friday within the Octave of Christmas?
The short answer is YES, this year, yes.
According to Canon Law, Catholics are bound to do penance on Fridays of the year except when the Friday is of the liturgical rank of a “Solemnity” (a new-fangled post-Conciliar rank).
In some years, the Friday will be 1 January. That’s another matter, because 1 January is the Solemnity of Mary, Mother of God in the new-fangled calendar, and the Solemnity removes the obligation.
THIS YEAR, however, Friday is the Sixth Day in the Octave.
The Octave of Christmas does not have the same liturgical “weight” of the Octave of Easter.
Easter Friday (a Solemnity) outweighs the penance thing, but Christmas Friday does not.ASK FATHER: Must we do penance, abstain from meat, on Friday in the Octave of Christmas? | Fr. Z’s Blog