Depends on the breed, the conditions she lives in, her age, her general health, etc. There is no set time. I do think, in general, she will begin to slow down toward the beginning of the second year of life, but will continue laying for years to come, if she is well. I have some who are four years old and though they have eased off some, they still lay several eggs a week when not molting. Someone here had a hen up in her teens (17, I think, when she died) who still laid an egg every so often.