Hi, the stated page yields for genuine Brother cartridges are based on the ISO testing standards. The number of pages that can be printed with a cartridge is affected by several factors, including paper size, number of pages per print job, amount of print on each page, font size, and print content (graphics, charts, etc.). Print jobs with large text fonts, graphics, charts, and/or large amount of solid coverage (black or any given color) will use much more toner and will shorten the life of the toner cartridge. If you have any questions about your Genuine cartridge, please contact Brother customer service at www.brother-usa.com/support.