Brother MFC-8440 B - Manual (Page 220)

S - 7 SPECIFICATIONS
Consumable items
Toner Cartridge Life
Expectancy TN-540: Standard Toner Cartridge - Up to 3,500*
pages
TN-570: High Yield Toner Cartridge - Up to 6,700*
pages
* (when printing letter size or A4 paper at 5% print coverage)
Toner life expectancy will vary depending upon the
type of average print job.
Drum Unit Life
Expectancy Up to 20,000 pages/drum unit (DR-510)
There are many factors that determine the actual
drum life, such as temperature, humidity, type of
paper, toner you use and number of pages per print
job.