it's his/her birthday
Es su cumpleaños la semana que viene.
It's her birthday next week.
Tomorrow is his birthday.
Me olvidé cuándo es su cumpleaños.
I forgot when her birthday is.
Sabíamos que hoy es su cumpleaños.
We knew that today is their birthday.
Usted sabe que es su cumpleaños mañana ¿verdad?
You know it's your birthday tomorrow, right?
— Train to Busan (2016)
Deberíamos salir con mamá el viernes porque es su cumpleaños.
We should go out with Mom on Friday because it's her birthday.
— Love Actually (2003)
Simplemente porque es su cumpleaños, piensa que puede hacer lo que le gusta.
Simply because it's his birthday, he thinks he can do whatever he likes.
— La canción del mar (2014)