Külli Reinumägi (née Külli Koik; born February 25, 1974 in Tallinn) is an Estonian actress.

Külli Reinumägi graduated from the Estonian Academy of Music and Theatre in 1996. After graduation, she began her stage career at the Estonian Drama Theatre. Later, she has continued her acting career as a freelancer and is one of the leaders and creators of the creative association MTÜ Oma Lava with Liia Kanemägi. In addition to theatrical role, Reinumägi has played in several television series, radio plays and films.

Reinumägi is married to film producer Alvar Reinumägi.