According to the document of Pope Saint John Paul II, as amended by Pope Benedict XVI:

“37.n I furthermore decree that, from the moment when the Apostolic See is lawfully vacant, fifteen full days must elapse before the Conclave begins, in order to await those who are absent; nonetheless, the College of Cardinals is granted the faculty to move forward the start of the Conclave if it is clear that all the Cardinal electors are present; they can also defer, for serious reasons, the beginning of the election for a few days more. But when a maximum of twenty days have elapsed from the beginning of the vacancy of the See, all the Cardinal electors present are obliged to proceed to the election.”

The moment that the See became vacant was the time of the death of Pope Francis: 21 April 2025 (Easter Monday), at 07:35 Rome time. Then a full day means a calendar day, so 22 April is day 1 and the 15th full day would be May 6th. This would place the start of the Conclave as early as May 7th. Note that the Cardinals can “move forward the start of the Conclave”, meaning they can move it to an earlier date, if all the electors are present.

Then the 20th day is May 11th. Since the text says “when a maximum of twenty days have elapsed”, the 20th day has elapsed at the start of the 21st day, May 12th. That is the latest day for the Conclave to begin.

So the Conclave should begin as early as the day of May 7th, or as late as the day of May 12th, or any day in-between. It is possible for the start day to be earlier, but that appears unlikely right now.

UPDATE: Vatican News is reporting: “The conclave to elect the 267th Pope will begin on May 7th, following the conclusion of the Novemdiales Masses to pray for the eternal repose of the late Pope Francis.”

Ronald L Conte Jr