Billie said that "Wake Me Up When September Ends" is about how his father's death affected him when he was just 10 years old. His father died of oesophagal cancer in September 1982. On The Howard Stern Show, we learn that afterward, Billie wouldn't leave his room. When his mother encouraged him to leave it, he simply replied, "Wake me up when September ends."

The song came out on Green Day's album American Idiot, released in 2004. But "Wake Me Up When September Ends" was also released as a single the following year.

"I think about him every day," Billie said on the show. "I kind of avoided writing about him for many years, and then finally had a breakthrough. It felt good. It wasn’t a negative emotion so much, but just honoring him." He also said that when huge events like that happen at such a young age, it's almost like starting life again at "year zero."