Before really delving into this, one needs to think about why you would write a novel in the first place.
Do you horseback ride? How much do you get paid for that? Do you ride a bike? How much do you get paid for that? Play an instrument? Read? Go to restaurants?
You get the idea. You should not be in this primarily, or secondarily, for the money. Sure you might get lucky and get paid to read books, or write restaurant reviews. But, what are the odds? You really won’t get paid to write.
It has been said, ad nauseam, that writing novels (or fiction in general) is a labor of love, not economics. You get it, you say. You still want to know how much the average novelist makes.
Very, very, little. No benefits and other costs add up. Your average “midlist” novelist, who has not been picked up by a large publisher makes $4,000 per book—before expenses! Note I said midlist also. Midlist means you have some name recognition. Per book can be spread out over multiple years. You will make in the hundreds with your first book at a tiny press. If you are lucky. It may only be in the tens or twenties. With the economies of books these days double digits is not all bad.
Your first book is both a labor of love and a learning experience. Second books are applying the learning and proving you really love the work. Third book you are telling the world you are serious about this. If you are serious about making this into a career, remember the 10,000 hour rule. The corollary for career in writing is don’t get excited until you sold your first 10,000 books—in one year.
You will see some other averages out there, such as U.S. department of statistics on authors. That includes ALL authors, including salaried authors (e.g. full time employees of Time Magazine). That average is $10,000 per year. Remember, this is the average that includes authors who get paychecks and includes the Stephen Kings of the world! Those making a comfortable living are rare and they put out multiple books per year, for tens of years.
So you want to be a writer? Tell me why—and don’t quit your day job!