With more than 2 million copies sold on the first day of its release, Half-Blood Prince broke all British sales records. British sales of Half-Blood Prince were 13 percent higher than for the first 24 hours of Order of the Phoenix.
According to Richard Knight, the managing director of Nielsen BookScan:
Typically, a good book will take about four to six months to go gold and very few books reach platinum in their first year of publication. Harry Potter and the Half-Blood Prince achieved platinum in less than one day!