First, I decided the entire novel should be roughly twenty chapters. After trying to sum up the draft chapters I'd already written, I wrote out what the next couple of chapters ought to be, then realized I needed to work backwards, using the long synopsis as a guide. Each paragraph in the synopsis seemed chapter-like. This worked great! Until I found I had a three-chapter gap in the middle. But maybe the novel won't work out that way...I am not sure how the length will work out, because, pantser.
Meanwhile, I am mentoring someone on finishing her own manuscript. Oh, well. Am doing my best.