That is a pretty tough question to answer. It will depend on the time of year, the feed you are feeding them, their environment, the health in their bloodlines, you get the idea.
I would guess anywhere from 10-12 in the warmer seasons. Figure each hen should have at least 1 day a week that they will not lay. In the cooler months, I would say 10 or less. Again, this is my best guess. Hope you get many more!