Rowling rose to great financial success thanks to her series of Harry Potter books, earning her a spot on the Forbes list and an estimated net worth of $1 billion (£638 million).
The Daily Telegraph reports that in the years since, Rowling's earnings have dwindled.
Rowling has given around $160 million (£102 million) of her money away to charity and has also been heavily taxed, leaving her with a fortune of just under $640 million (£408 million).
The author recently announced that she is tackling an adult novel, her first since completing the Potter series.
Pottermore, her interactive website for fans of the books, is due to launch this April.
Watch the trailer for Harry Potter and the Deathly Hallows: Part 2 below: