It has been stated by Eiichiro Oda one piece is about 80 percent finished (for manga). Doing some calculations it seems only about 200 chapters are left . There are 52 weeks a year so If one chapter comes out every day it would take around four years for one piece to end.
What percentage of One Piece is finished?
Is there any estimated percentage of the One Piece manga/anime completed? - Quora. Yes, the writer Oda himself said in an interview that the manga of one piece is actually 70% complete.