When planning to write a novel, advice comes from many sources—friends, fellow writers, and of course, one’s own research. Sage advice often stresses, “Write what you know.” That’s sound advice for sure, but if your motivation to write is to have many people buy and read your work, you must know what people are reading. Below are the top five book genres earning the most money. The figures are based on leading authors’ earnings and industry trends as researched by the 
Romance Writers of America Association.
#1 Romance / Erotica ($1.44 billion)
Fifty Shades of Grey pushed author E.L. James to a net worth of $60 million, while Danielle Steel claims to be worth $610 million. All that wealth comes from formulaic romance novels that feature similar story-lines and endings.
#2 Crime / Mystery ($728.2 million)
Many of these novels come in sagas and trilogies featuring the same protagonist. Readers are fascinated by stories of murder and violence, and in fact, true crime stories are the most popular.
#3 Religious / Inspirational ($720 million)
No surprise here that the ultimate bestseller has always been the Bible. But many readers want answers to life’s problems and want to feel good about themselves and their fellow-man. Wholesome stories of redemption and reward continue to be popular.
#4 Science Fiction and Fantasy ($590.2 million)
Lord of the Rings and The Hunger Games—tremendous bestsellers and movies. These tales draw both young adult and adult audiences. The fact that the stories are continuing sagas make them lasting and appealing.
#5 Horror ($79.6 million)
Some folks enjoy being scared. Storytellers Stephen King and Dean Koontz have popularized this genre, and have had their most popular novels hit the big screen.
After reading the above astounding figures, the rest of us need a dose of reality. The Guardian, a British newspaper, advises that most writers earn less than $1,000.00 per month. Hardly a living wage. Who knows the reason(s) why some succeed while others do not? However, there is a bright side to the book industry. Now that ebooks have become increasingly popular, self-published authors now account for 20% of sales in the genre market. Moreover, even if your expertise or interest falls outside of the five most profitable genres, isn’t it worth the effort to try one? Why not write a romance novel or mystery? Sometimes writing beyond one’s comfort zone results in success. Besides, what do you have to lose?
John M. Wills 
If you’re writing for money, you might as well forget it. (Unless you do write something like 50 Shades of Gray.) In most cases, the motivation to write is something far different than monetary gain or fame. I write because I must. Good post, John.
Spot on, Marilyn. But one can never predict when one of their books will hit the big time, if ever. Thanks.
That’s interesting to know, John. I’ve written in three of those genres and I know you certainly have. Like Marilyn, I didn’t go in it for the money, which is fortunate. My first book needed to be out there and the next one just came about over many, many years. I consider the ability to write “a gift”, so I write because I’ve been blessed with the ability to do so.
And you write well, Jackie.