One of the most common questions asked by Catholics is, "How often should a Catholic go to confession?"
The answer is both straightforward and complicated at the same time.
Minimum requirement
According to Canon Law the bare minimum is once a year.
After having reached the age of discretion, each member of the faithful is obliged to confess faithfully his or her grave sins at least once a year. (Canon 989)
However, this requirement is tied to the reception of Holy Communion, as the Catechism of the Catholic Church explains.
The second precept ("You shall confess your sins at least once a year") ensures preparation for the Eucharist by the reception of the sacrament of reconciliation, which continues Baptism's work of conversion and forgiveness. (CCC 2042)
With this in mind, the Catechism further explains that in order to properly receive Holy Communion, one must always confess grave sins beforehand.
The Lord addresses an invitation to us, urging us to receive him in the sacrament of the Eucharist: "Truly, I say to you, unless you eat the flesh of the Son of man and drink his blood, you have no life in you."
To respond to this invitation we must prepare ourselves for so great and so holy a moment. St. Paul urges us to examine our conscience: "Whoever, therefore, eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord. Let a man examine himself, and so eat of the bread and drink of the cup. For any one who eats and drinks without discerning the body eats and drinks judgment upon himself."
Anyone conscious of a grave sin must receive the sacrament of Reconciliation before coming to communion.
Grave sin
Basically, you are "required" to go to confession once per year, if you intend on receiving Holy Communion once per year. On the other hand, if you desire to receive Holy Communion on a weekly or daily basis, then you will need to go to confession every time you are "conscious of grave sin."
It is recommended, though not required, to confess venial sins; this is often the reason why Catholics will go to confession on a weekly or monthly basis.
In the end, confession is a beautiful sacrament of God's mercy and should not be looked at as a "requirement," but as an "opportunity" to receive God's love. It gives us the ability to repair our relationship with God and with the Church, opening us up to a shower of God's grace.
We should confess because we love God, not because we "have to," though the requirements are there to lead us along the path of eternal life.