Female chickens are called pullets for their first year or until they begin to lay eggs. For most breeds, around 20 weeks is a typical age for the first egg.
Some breeds lay eggs daily, some every other day, some once or twice a week.
Some individual hens never lay eggs, due to narrow pelvises or other anomalies.
Normal laying routines can be interrupted by molting, temperature extremes, illness, poor nutrition, stress, or lack of fresh water. Hens usually return to normal laying habits when the disruption-causing factor ends or is corrected.
Most hens are productive layers for two years before declining in production, but some continue to lay eggs for several years.
Hens will lay eggs whether or not they’ve ever seen a rooster. Roosters are necessary only for fertilization of eggs.