From Pope’s declaration, the Vatican, 10 February 2013 :
After having repeatedly examined his conscience before God, he has come to the certainty that his strengths, due to an advanced age, are no longer suited to an adequate exercise of the Petrine ministry.
He is well aware that this ministry, due to its essential spiritual nature, must be carried out not only with words and deeds, but no less with prayer and suffering. He has had to recognize his incapacity to adequately fulfill the ministry entrusted to him.
For this reason, he renounces the ministry of Bishop of Rome, Successor of Saint Peter, entrusted to me by the Cardinals on 19 April 2005, in such a way, that as from 28 February 2013, at 20:00 hours, the See of Rome, the See of Saint Peter, will be vacant and a Conclave to elect the new Supreme Pontiff will have to be convoked by those whose competence it is.