Can chicken eggs hatch after the 21 days?

Chicks will not always hatch out on the 21st day. Sometimes we have had to wait an extra week for the chicks to hatch, however this could be due to us not marking the correct date on the calendar. If the Mother Hen gets off the nest make sure you crack the eggs open (With extreme care) as the chicks could still be alive and ready to come out. If the hen is on the nest for 4 weeks i'd recommend taking her out and ensuring she doesn't go back on as this is extremely bad for her health.