This smooth R&B jam finds Disclosure, Kehlani and Syd from The Internet pondering a relationship quandary: Is it okay to call your ex on their birthday? Howard explained in a press release: "Syd and I were going through a similar thing at the time, trying to work out if it was cool to call your ex to say hi or is it too awkward/mean to do so out of the blue?"
"Birthday" is the oldest track on the Energy album. Guy and Howard Lawrence sketched the song during a day off in Los Angeles in 2018. "I love how it's almost two-step garage, but it's got a dubstep kind of tempo and it's almost R&B," Guy told Apple Music. "It actually has an old-school Disclosure sound going on."
Disclosure worked with Syd on the song during their time in LA but Kehlani sent her vocals over later via a digital file. Howard admitted to Apple the brothers dislike recording remotely, but made an exception in this case. "We prefer to write together so we can creatively collaborate because we're very particular," he said. "But when Kehlani sent her verse over, it was so perfect that there was literally nothing I could change. I tried, to be fair, but I was making it worse. So we made an exception - just for Kehlani."