Billie Eilish sings about the aftermath of a car accident that involved someone close to her. Much to Eilish's relief, the loved one survived the crash. The incident took place on November 30, hence the song title.
Rather than recounting the events in a linear narrative, Eilish starts off the song a few weeks after the accident. When the person struggles to remember what happened, the singer reminds them they called her before the terrible event and the conversation they had in the hospital.
In the second verse, Eilish recalls a journey on Interstate 5 in California. Stuck in a traffic jam, she noticed an accident caused the standstill but continued traveling. Late that night, Eilish realized the ambulances she'd seen on the hard shoulder had been for this person.
Eilish then expresses her gratitude nobody died. The car accident could have had horrific consequences in different circumstances, but the person is alive and nobody else got hurt.
The experience terrified Eilish, prompting the singer to write "The 30th," her first song since the release of 2021's Happier Than Ever. "Something happened on November 30 and it had just been the most indescribable thing to have to witness," she told Apple Music. "I had been writing down all these thoughts that I was having. I was with Finneas, and I was like, 'I'm sorry, I don't know what you were planning on doing, but we need to write this song about this right now.' And we did."
"The 30th" is one of two tracks from Eilish's Guitar Songs EP, released on July 21, 2022. Both this song and the other tune, "TV," mainly comprise the sound of Eilish's soft voice and Finneas' acoustic guitar. Eilish said the goal with Guitar Songs was to "go back to the way that it was at the beginning," when the sibling duo started writing together, in their parents' Los Angeles home. "We were just making music, writing songs on Finneas' guitar in our parents' house and then showing them to people," Eilish said. "That's our roots. That's how Finneas and I started writing music - on an instrument with just us."
