(crossposted from simplyexplained.com)

Under the Code of Canon Law, #917 through 921. notwithstanding the exceptions noted, may one receive Holy Communion outside of Mass? For example, one receives Holy Communion before Mass, because he or she can not stay for a Mass due to a prior personal commitment, say a doctor”s appointment. Or, one comes to Mass late, without good reason, to receive Holy Communion.

I am not a canon lawyer. You should consult one for definitive legal advice.

Canon #918 states

It is most strongly recommended that the faithful receive holy communion in the course of a eucharistic celebration. If, however, for good reason they ask for it apart from the Mass, it is to be administered to them, observing the liturgical rites.

As far as I know, “good reasons” only include severe restrictions such as illness which renders the person non-ambulatory. I would think that other personal commitments of a “normal” or commonplace nature are not sufficient justification for transgressing Church law.

Furthermore, from a more spiritual standpoint, one must consider whether one’s priorities are rightly ordered when one willingly chooses something over the very person of Christ himself, his very Body and Blood, Soul and Divinity.

See also this good reference article by Fr. William Saunders from the Arlington Catholic Herald.