Sometimes we get so far into our stories that we don’t know when to end. How do we know? When you put all facts and emotions into the book. Don’t go on after the plot is explained and the characters find their way to discovering which path to go on after the ending. Maybe you can lead into what they did with their lives after in short paragraphs, but don’t let it start up another part of their life.
Make sure everything is covered that you brought up in the book. Give an end to each event and why it happened. After years of writing, you will feel the ending with a comfort without needing to add page after page to explain the story.