"Birthday" is a song by American pop singer-songwriter Katy Perry. It is the third track from her fourth studio album, Prism (2013). "Birthday" was released as the third single from Prism on April 21, 2014. The lyrics are about celebrating a partner's birthday while Perry makes sexual references.
It was released on April 21, 2014, and the song became a moderate success. It peaked in the top ten in Canada, the top twenty in the US, and the top twenty-five in the UK. On July 27, 2015, the Recording Industry Association of America certified the song Platinum for sales and streams equal to one million copies shipped.