User blog comment:Manuel de la Fuente/Hajime Isayama talks about the ending of Attack on Titan (June 2016 interview)/@comment-28954877-20160626193142/@comment-5774380-20160626210857

Around 30 chapters at most. Personally, I don't think it will end in December 2018, but more likely between February (chapter 102, two arcs of 16 chapters, Volume 25) and October (chapter 110, two arcs of 20 chapters, Volume 27).