According to CBR, in order for the movie to break even is $600 million when everything is factored in. Production budget ($250 million, plus $25 million in reshoots, then there's the millions spent on promotion costs).
And considering the movie already has mixed reviews and a 43% (currently) rating on Rotten Tomatos, this movie isn't going to be the success the CW wish it to be.
That makes Justice League look like it'll have a total domestic gross around the $220 million ball park. In comparison, Thor: Ragnarok should make it to at least $300 million domestically. Justice League is doing well in foreign sales though and might make it to $600 million world-wide. By my estimation, that means Warner Bros. will lose $100 million before considering ancillary sales of merchandise, cable revenue, and discs.