Asking a writer how close their book is to being done is like asking an artist how close their painting is to being ready, or a computer programer how much time they need to finish a project. You cannot put a timeframe on creative output. It’s done when it’s done.
I’m sure once I’ve written multiple books, I will have a better gauge, but for now, I have no way of knowing how long or how close I am. I can estimate, I can work towards a given timeline, but until I’m in my final stage of editing (fixing grammer, not content), I won’t really know.