Excommunication

If I've committed a sin and the penalty is automatic excommunication and I didn't realize the penalty was automatic excommunication but I knew it was a sin and now I regret it and want to go to confession to confess it, will I be excommunicated after I confess?

Thank you for that question. I would like to use this opportunity to clear up a large misconception about excommunication. Being excommunicated does not been you have been "kicked out" of the Church. Rather, excommunication is a strong, remedial penalty given with the hope that it’ll wake the sinners up and move them to true repentance — and back into full communion with the faithful.

the grounds for excommunicationare as follows: You have committed a grave offense that caused you to be spiritually separated from the Church and the community of the faithful. You have left the Church on your own accord by committing the offense. 

Some offenses warrant excommunication as a result from an authority, such as a diocesan tribunal.  Others are automatic (effective at the moment the act is committed) and without the intervention of the Church. Catholics are automatically excommunicated for committing these offenses:

• Procuring of abortion
• Apostasy: The total rejection of the Christian faith.
• Heresy: The obstinate post-baptismal denial of some truth, which must be believed with divine and Catholic faith.
• Schism: The rejection of the authority and jurisdiction of the pope as head of the Church.
• Desecration of sacred species (Holy Communion)
• Physical attack on the pope
• Sacramental absolution of an accomplice in sin against the Sixth and Ninth Commandments
• Unauthorized episcopal (bishop) consecration
• Direct violation of confessional seal by confessor

The local bishop has the authority to remove most excommunications, but many bishops delegate this power to all their parish priests when it involves a penitent confessing the mortal sin of abortion.  This way, the person going to confession can simultaneously have the sin absolved and the excommunication lifted. This is to make it easier for people to go to confession and reconcile themselves with God and the Church, especially after a very emotional, personal, and serious matter, such as abortion.

Some excommunications, however, are so serious that only the pope or his delegate can remove the penalty. For example, if someone desecrates (shows irreverence to) the Holy Eucharist, only the pope can remove that excommunication. Likewise, if a priest attempts to absolve someone guilty of breaking the Sixth or Ninth Commandment with whom he himself participated in that sexual sin, his excommunication is automatic and reserved to Rome. So, too, a bishop who ordains a priest to the order of bishop without prior orders from the pope is automatically excommunicated, and only the pope can remove that excommunication, which applies equally to the ordaining bishop and the bishop being ordained.

I sincerely hope this helps. My best advice to you would be to receive the Sacrament of Reconciliation and let the priest give you direction.