The Catholic Encycolpaedia states that excomminication is imposed latae sententiae on "All apostates from the Christian Faith … to such apostates are assimilated those who publicly renounce all religion. After I became a lapsed Catholic, I stated to friends and family that I rejected all religion, and also participated in online discussions maintaining an atheist stance. Does this mean that I have been excommunicated? If so, what steps must I take to rejoin the Church? Thanks for your help.
No, you have not been excommunicated. In order to be excommunicated one must know what constitutes it and then will it. All you need to do is go to Confession. As a repentant sinner, you will be the cause of rejoicing in heaven. Welcome back!
Fr. Vincent Serpa, O.P.