"The 30th" is a song by American singer-songwriter Billie Eilish. It is one of two tracks from her second extended play (EP), Guitar Songs, released as part of a double single on July 21, 2022. She wrote the song with its producer, her brother Finneas O'Connell, on December 30, 2021. They did so after Eilish recalled seeing her friend experience a car accident one month prior and felt the need to write about the event immediately. Despite planning to begin work on her subsequent album, she decided not to include the song in its track list, partly out of a desire to share its message as soon as possible.