The two-part drama, "Harry Potter and the Cursed Child," is a smash hit in London and is scheduled to open on Broadway next year. A book based on the play was an instant No. 1 best seller. Warner Bros. recently licensed the television rights to the Harry Potter films to NBCUniversal for as much as $250 million.
Any estimate of Ms. Rowling's fortune is at best informed speculation, and most previous attempts I've seen don't seem very informed. Ms. Rowling is famously private, especially about her financial and business affairs. She denied being a billionaire after Forbes first anointed her, telling the television interviewer Katie Couric in 2005 that "I've got plenty of money, more money than I ever dreamed I would have. But I am not a billionaire." She has remained publicly silent on the subject since.
So I set out this week to assess the size and scope of her fortune, not to invade her privacy but because she's that all-too-rare commodity in the ranks of the ultra-wealthy — a role model. Not only has she made her fortune largely through her own wits and imagination, but she pays taxes and gives generously to charity. At a time of bitter disputes over rising income inequality, no one seems to resent Ms. Rowling's runaway success.
"It's an impressive story," said Steven N. Kaplan, a professor at the University of Chicago Booth School of Business and an author of "It's the Market: the Broad-Based Rise in the Return to Top Talent," a study of wealth generation in the digital age.
"She struggled as a single mother," he said. "Then, she created this amazing franchise. She had tremendous talent, and she's reaping the rewards. People don't mind that. What they resent is when chief executives get paid for failure."
Ms. Rowling has also been backed by some high-powered negotiating and marketing muscle — Scholastic, which published the Potter books; Warner Bros., the studio behind the Potter films and now the "Fantastic Beasts" franchise; and NBCUniversal, which opened the Wizarding World attractions at its theme parks. Neil Blair, a former Warner Bros. executive, has represented her and fiercely protected her interests since he founded the Blair Partnership, a literary agency, in 2011, with Ms. Rowling as his most prominent client. Mr. Blair did not respond to requests for comment.
Along with other famous authors, entertainers and sports stars, Ms. Rowling has also benefited from globalization and technology advances, the same forces that have squeezed the working class. "Thirty and 40 years ago, entertainers and sports figures didn't have that kind of money," Professor Kaplan said. (He noted that Bob Hope was the only entertainer on the original Forbes 400, and he made most of his money in real estate.) "Thanks to globalization, the internet and social media, they can reach a much bigger market today," he said.
A close look at Ms. Rowling's sources of income suggests that she's worth more than $1 billion, even allowing for a large margin of error. I came up with the estimates by interviewing a range of publishing and entertainment executives and agents. Some of them have negotiated with Ms. Rowling's representatives and knew what terms they were seeking. No one was willing to be identified because pretty much everyone hopes to do business with Ms. Rowling. "She's a sacred cow," one executive said.
To start with the obvious, there's the source of her wealth: The seven Harry Potter books have sold an estimated 450 million copies, with estimated total revenue of $7.7 billion. At a standard 15 percent author's royalty, she would have earned $1.15 billion. These books continue to sell strongly years after they were first published.