How does the counting of days work? When we say they "hatch on day 21", does that mean that they hatch in the 21st day (leading up to 21 days completed), or when 21 days have been completed (in the day leading up to 22 days completed). Like "Day 1" is counted as UP TO one day complete OR the day following 1 day completed? For instance, we call a child has completed one year of life "1", not a child in the first year of it's life. I hope I am explaining myself right here. And i do realize that chicks can hatch early or late, but I am looking for the optimum hatch date if all goes right. On Thursday night my chicks will have completed 21 full days of incubation. Last night (completed 19 days of incubation) they were all rocking and one piped. I assumed that they weren't due until Friday (Thursday night marks 21 days COMPLETED). Was I wrong? When would they be due?