Like “Roar”, this song was a return to the upbeat sound of Perry’s early work, and after her dreary attempts as ‘seriousness’ on songs like “Dark Horse”, “Unconditionally”, and “By the Grace of God”, that certainly came as something of a relief at the time. But the fact remains that this is an incredibly stupid song (it’s basically a distaff version of Jeremih’s infamous “Birthday Sex”). Granted, some of the songs from Perry’s early career were equally stupid (“Hot N Cold” being one obvious example), but those songs were also extraordinary catchy, which helped elevate their idiocy into the realm of the enjoyably bad. By contrast, the melody of “Birthday” is only moderately catchy, and not really enough to compensate for its gaping flaws.
Verdict: Perry had done worse around this time (and has certainly done worse since), but this is still pretty bad.