While one theory states that his mother Anahobe no Hashihito no Himemiko gave birth to him at her real mother Oane no Kimi's parent's house, i.e., the house of his uncle SOGA no Umako (Umako=lit. Son of Horse), and he was named after 'the residence of Umako,' the most convincing theory at present states that he was named after the place named 'Umayato' near his birth place.
また母親の穴穂部間人皇女（あなほべのはしひとのひめみこ）が実母（小姉君）の実家で出産したため、つまり叔父にあたる蘇我馬子の家で生まれたことから馬子屋敷が転じて厩戸（うまやと）と付けられたという説もあるが、現在のところ生誕地の近辺に厩戸（うまやと）という地名があり、そこから名付けられたという説が有力である。