J.K. Rowling’s annual earnings in 2007-2008 were estimated to be US$300 million (£150 million) according to the 2008 Forbes Celebrity 100 list released on 11 June 2008.
From Forbes: “It was wizardry that transformed J.K. Rowling from a destitute single mother on welfare into a best-selling billionaire. Her adventures of teenage magician Harry Potter and his classmates at Hogwarts became a children’s literary sensation in 1998 with the U.S. publication of Harry Potter and the Sorcerer’s Stone. It and the six subsequent books have now sold 375 million copies worldwide. The final one, Harry Potter and the Deathly Hallows, has sold 44 million since it was published last July, including 15 million in the first 24 hours.”