Due to lack/damage of historical records in patches of Catholic history it is argued that only about 4-10 popes have “resigned” their office. Below is a list of some of those and why.
1) Pontain (230-235) abdicated before being sent to work in the mines by Roman Emperor Thrax
2) Marcellinus (296-304) *controversial* prayed to pagan gods
3) Silverius (536-537) forced to abdicate by Emperor Justinian
4) John XVIII (1003-1009) ?
5) Benedict IX (confusing) elected, ejected, returned, abdicated, deposed, returned, ejected, excommunicated
6) Celestine V (1294) only 5 months but established law that allowed popes to resign
7) Gregory XII (1406-1417) resigned to help unify the church due to the Schism
Feb 28th will begin the Interregnum period which transfers powers to the College of Cardinals.
March 15th will begin the Election process