According to an interview with Yomiuri Shinbun magazine, One Piece creator Eiichiro Oda revealed that the storyline of the most popular manga of all time is finished at around 80 percent!
Here’s a graph of the author’s predictions over the years of when the series will end:
It’s really interesting now trying to gauge how much is left of the story. We’ve just begun Wano, which should be a long arc, but might not be considering it’s part of the same saga as Whole Cake Island. The Dressrosa saga was roughly 150 chapters long, most of the main sagas thus far have been 100-150 chapters long. The current saga, the Yonko saga, is already over 100 chapters long so if Oda sticks to his usual length of sagas, Wano won’t be more than 50-60 chapters at most.
After Wano, there’s several key beats to the story that need addressing: Elbaf, Shanks, World Government, Revenge vs Akainu, Revolutionary Army, Blackbeard, Raftel and if we’re going to take what characters in the manga say as gospel for us readers, the war to come once Raftel is reached.
Probably Oda will handle all of those massive story beats in not less than 300 chapters. I think once the Yonko saga wraps up, probably around chapter 940-950, we have two more sagas to come MINIMUM, so we can estimate that from the current point, we have another 350 chapters minimum, which is almost seven years. So if Oda doesn’t change his patterns, One Piece will keep going for almost another decade.