At what age do dogs usually get their period?

A female dog usually starts estrus and menstruation at about 8 months, and the bleeding lasts 7-14 days. Dogs come into heat twice a year, every six months, but due to individual differences the timing and duration vary, and bleeding amount differs by size. Small dogs usually bleed little and lick the discharge clean, so owners may barely notice; large dogs bleed more, and the owner can put sanitary pants on them during the period.