What is the incubation period for a domestic chicken egg?

The incubation period for a domestic chicken egg is about 21 days.

During incubation, the embryo develops inside the fertilized egg while warmth and humidity are carefully maintained. A broody hen naturally provides heat by sitting on her clutch, while commercial hatcheries use machines that control temperature, humidity, ventilation, and egg turning.

The 21-day figure is an average for domestic chickens, not a rule shared by every bird. Temperature, humidity, genetics, and handling can affect the exact hatching time. Eggs sold for eating are normally unfertilized and therefore cannot hatch simply because they are kept warm.

Chicken embryos develop through recognizable stages, including formation of the circulatory system, limbs, feathers, and beak. Near hatching, the chick uses a temporary egg tooth on its beak to break through the shell. The egg tooth is a small projection, not a permanent tooth.