The series was officially picked up on May 6, 2015, and received a full season order on November 30, 2015. On May 12, 2016, Warner Bros. Television announced that the series had been renewed for a second season and that it would move from CBS to The CW, where it debuted on October 10, 2016. On January 8, 2017, The CW renewed the series for a third season, which began airing on October 9, 2017. As of February 5, 2018, 55 episodes of Supergirl have aired.

When is super girl season three coming out? Okie... think carefully first, then make a decision:
To answer the question, consider the following: On January 8, 2017, The CW renewed the series for a third season, which began airing on October 9, 2017. So, the answer is October 9 , 2017.