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.
Note can. 1251 in the 1983 Code.
Can. 1251 Abstinence from meat, or from some other food as determined by the Episcopal Conference, is to be observed on all Fridays, unless a solemnity should fall on a Friday. Abstinence and fasting are to be observed on Ash Wednesday and Good Friday.
Remember, you can ask your parish priest to dispense you or commute acts of penance.
Can. 1245 Without prejudice to the right of diocesan bishops mentioned in can. 87, for a just cause and according to the prescripts of the diocesan bishop, a pastor [parish priest] can grant in individual cases a dispensation from the obligation of observing a feast day or a day of penance or can grant a commutation of the obligation into other pious works. A superior of a religious institute or society of apostolic life, if they are clerical and of pontifical right, can also do this in regard to his own subjects and others living in the house day and night.
Members of religious communities and third orders should consult their own regulations and review to whom they turn for dispensations.
Also, you can substitute another form of penance for abstaining from meat. Make it penitential, however. Abstinence from meat has good reasoning behind it. For some, however, there abstinence from other things can be of greater spiritual effect.
Also, it may be that some local places have exceptions in their calendars. For example, if, this year, you are a parishioner of a parish named in honor of St. Exuperantius, Martyr, (Feast 30 Dec.) your patronal feast could be a reason not to be bound by Friday penance.