What days do eggs hatch?

[jkp11]

I have always heard it takes 21 days for a chicken to hatch, but lately other people have told me they can hatch as early as day 18 to as late as day 28. Is this true? Isn't that unhealthy?

 

[math ace]

21 days is the timing for perfect conditions with chicken eggs. They can come a day or so early if the temps are running high and a day or too later if the temps are running low. NO ONE sets out trying to make them come early or late, but it does happen.

 

[kara_leigh]

My broody hen was sitting on 5 eggs. One hatched yesterday (day 20), two today (day 21), and it looks like two will hatch tomorrow (day 22, they have pipped).