When will my female dog experience her first heat or period?

The size of your dog can determine when her first heat will be. Small breed of dogs reach puberty around six months of age… whereas larger breeds may reach puberty a little later (around 8-12 months of age). Your female puppy’s first heat cycle will last about 21 days, and she will continue to go into heat on the average of every six months, usually in the late winter and summer.