Is It A Mortal Sin Not To Go To Confession Once A Year?

Q: When I learned the second precept of the Church, as a child it was “To go to Confession once a year if you have mortal sin.” The current Catechism states on the 2nd precept: “To go to confession at least once a year” (#2042). Have the Bishops, changed the 2nd precept on their authority? 

A: The catechism, while less than exact in the quote you supply does footnote Canon 989 for greater precision, which says: All the faithful who have reached the age of discretion are bound faithfully to confess their grave sins at least once a year.

The Catechism states elsewhere: According to the Church’s command, “after having attained the age of discretion, each of the faithful is bound by an obligation faithfully to confess serious sins at least once a year.” Anyone who is aware of having committed a mortal sin must not receive Holy Communion, even if he experiences deep contrition, without having first received sacramental absolution, unless he has a grave reason for receiving Communion and there is no possibility of going to confession. (#1457).

Thus, there is no change in the precept, though one may admit the catechism could have been more precise in the text you cite.

That said, it may be of some pastoral advantage to remember that there is a tendency today to minimize the possibility and frequency of mortal sin. It is not hard to understand that most of the adult faithful out to be getting to confession more than once a year anyway. It is quite likely that most adults, even if not guilty of sins against life and sexual purity, are often guilty of rather serious sins against charity. It is quite possible to cause serious harm, and emotional or spiritual distress to people by harsh things we say. Further, lies can cause more than minimal harm, reputations can be tainted, people misled, and error flourish. Sins of omission through greed, neglect or laziness can also cause grave harm. Missing Mass is a mortal sin, and being significantly neglectful in handing on or defending the faith can also become quite serious.

More could be said here, but one ought not to causally dismiss that they should likely get to confession even more than once a year. Further the Church also encourages the faithful to confess frequently even if they are not aware of mortal sin since the Sacrament of Confession not only confers the grace of absolution, but also the grace to avoid sin in the future.