Last name Birthday (วัญญา 
, Birthday 
, เกิดวัน ) , all over the world, is a rare cognomen. The cognomen Birthday is habitual in Thailand, where it is a rare surname, Australia, where it is a very rare surname, and Canada. In absolute terms, the name is most common in Thailand, the United States, and China. Very seldom, Birthday is the forename as well as the last name.