|Photo credit Eric Rice
Calculating a chicken's point of lay is akin to looking on the back of a seed pack and seeing how many days it takes to harvest the vegetable you're thinking of planting. Some chicken breeds mature earlier than others, so you can take that into account as you're planning your flock.
Aspiring, but impatient, backyard egg farmers can buy pullets at "point of lay" which means they'll be enjoying fresh eggs within a week or so of bringing their hens home. But there's a cost to buying pullets at point of lay, and that's the cost of missing out on watching chicks grow up to be pullets and the imprinting of these chicks on you as their "mother hen."
So there's a bit more planning involved for those of us who are interested in raising our hens from the time they are day-old chicks. The 17-to-26 week guidance is a spread of a full 2 months, in other words, the difference between enjoying your first eggs on Labor Day or on Halloween(!).
Now, as you make plans to start raising chicks, remember to circle a date 4 and a half months after you bring them home as the day to start expecting eggs. Our Plymouth Rock chicks took 20 weeks to lay their first egg, and I have to admit those last three weeks of waiting (from week 17 to week 20) were excruciating!