JK Rowling has reportedly earned more than £600,000 (S$1.1 mil) a month in the past two years.
The 55-year-old author — who is is best known for writing the Harry Potter series — has earned as much as £637,321 a month over the last couple of years — in part, thanks to the success of her Cormoran Strike books, which have been turned into a TV series.
Rowling — who writes the Strike books under the name Robert Galbraith — raked in £12,850,000 in 2018 and £2,445,725 last year from a company that deals with her TV work, according to The Sun newspaper.
The Strike series, about a private eye of the same name, has been transformed into TV shows — called CB Strike — by her Bronte Film and Television production company.
The firm is also responsible for The Casual Vacancy series on HBO, as well as the Harry Potter show in London's West End.
The company turned over £18 million last year, according to accounts lodged with Companies House, which confirmed a significant increase from £13.5 million in 2018.
The accounts said: "Post lockdown, the company and the group is very well placed to deliver a strong financial result."
Meanwhile, Rowling previously admitted she doubted a publishing company would ever throw its support behind her Harry Potter books.
The novels have become one of the most successful franchises in history, but Rowling initially doubted whether the books would become a commercial success.
She said: "I did have a belief, with Harry, that the difficult thing would be persuading someone to take it, because it didn’t fit.
"People said children’s books had to be half the length, and what an old-fashioned subject, a boarding school. I did have this feeling that the difficult thing would be persuading someone to publish it - but that if it was, people would like it."