In the Catholic Church, does the private Act of Contrition require a specific prayer?

In the Catholic Church, does the private Act of Contrition require a specific prayer?

The short answer is no. In fact one is free to say an act of contrition of one’s own inspiration. You are not obliged to pray a specific act of contrition, when going to confession. They are written down in confessionals now-a-days as an aid for penitents in confession.

However, the Act of Contrition in absence of the ability of going to confession, especially if one is in the state of mortal sin should be a form of Perfect Act of Contrition, with the appropriate dispositions.

Not all acts of contrition are equal. Here follows some acts of contrition listed by the USCCB:

Act of Contrition

O my God, I am heartily sorry for having offended Thee, and I detest all my sins because of thy just punishments, but most of all because they offend Thee, my God, who art all good and deserving of all my love. I firmly resolve with the help of Thy grace to sin no more and to avoid the near occasion of sin. Amen.

(A traditional version)

or:

My God,I am sorry for my sins with all my heart. In choosing to do wrong and failing to do good, I have sinned against you whom I should love above all things. I firmly intend, with your help, to do penance, to sin no more, and to avoid whatever leads me to sin. Our Savior Jesus Christ suffered and died for us. In his name, my God, have mercy.

(from the Rite of Penance)

or:

Lord Jesus, Son of God, have mercy on me, a sinner.

(from the Rite of Penance)

One can find many more acts of contrition the world over!

But what is the difference between perfect and imperfect contrition?

Contrition may be either perfect or imperfect. While perfect contrition forgives all sins, it does not relieve us of the obligation to go to confession. The Catechism explains:

When [contrition] arises from a love by which God is loved above all else, contrition is called “perfect” (contrition of charity). Such contrition remits venial sins; it also obtains forgiveness of mortal sins if it includes the firm resolution to have recourse to sacramental confession as soon as possible.

The contrition called “imperfect” (or “attrition”) is also a gift of God, a prompting of the Holy Spirit. It is born of the consideration of sin’s ugliness or the fear of eternal damnation and the other penalties threatening the sinner (contrition of fear). Such a stirring of conscience can initiate an interior process that, under the prompting of grace, will be brought to completion by sacramental absolution. By itself, however, imperfect contrition cannot obtain the forgiveness of grave sins, but it disposes one to obtain forgiveness in the sacrament of penance. (CCC 1452–53)

According to Catholicism, those you have committed mortal sin, must confess their sins in kind and number to the best of one’s ability, to a priest in the sacrament of confession. Catholicism belief in the ability of ordained minister’s to absolve serious sins come from Our Lord’s own words.

Whose sins you shall forgive, they are forgiven them; and whose sins you shall retain, they are retained. - John 20:23

Is any man sick among you? Let him bring in the priests of the church, and let them pray over him, anointing him with oil in the name of the Lord.

And the prayer of faith shall save the sick man: and the Lord shall raise him up: and if he be in sins, they shall be forgiven him.

Confess therefore your sins one to another: and pray one for another, that you may be saved. For the continual prayer of a just man availeth much. - James 5:14-16

Here follows a simple definition of Catholic sacramental confession:

The auricular confession of one's sins in the sacrament of penance. If they are mortal sins, it is required that they be confessed as to number, type, and such circumstances as affect the gravity of the sins committed.