From Wikipedia:

The Roman Martyrology assigns 29 June as the feast day of both Peter and Paul, without thereby declaring that to be the day of their deaths. St. Augustine of Hippo says in his Sermon 295: “One day is assigned for the celebration of the martyrdom of the two apostles. But those two were one. Although their martyrdom occurred on different days, they were one.”

This is also the feast of both Apostles in the calendar of the Eastern Orthodox Church.

In the Roman Rite, the feast of the Chair of Saint Peter is celebrated on 22 February, and the anniversary of the dedication of the two papal basilicas of Saint Peter’s and Saint Paul’s outside the Walls is held on 18 November.

Before Pope John XXIII’s revision in 1960, the Roman Calendar also included on 18 January another feast of the Chair of Saint Peter (denominated the Chair of Saint Peter in Rome, while the February feast was then called that of the Chair of Saint Peter at Antioch), and on 1 August the feast of Saint Peter in Chains.