The math
Chicken incubation is the most predictable schedule in poultry: 21 days from set to hatch, lockdown 3 days before. The interesting work is candling, humidity management, and not opening the lid when you shouldn't.
hatch_date = set_date + 21 days
lockdown_date = hatch_date - 3 days
Frequently asked
When should I first candle?
Day 7 is the sweet spot. Earlier and you can't see much; later and you start risking the embryo. Hold the egg against a bright light in a dark room. A fertile egg shows a dark spot with veins spidering out. A clear egg is infertile - pull it. A blood ring is an early death - also pull.
What about a broody hen instead of an incubator?
A committed broody hen does this job better than most incubators. She'll turn the eggs, regulate temperature with her body, and manage humidity through skin contact. Same 21 days. Watch for hens that abandon the nest after a few days - half-incubated eggs are not salvageable.
Why is my hatch late or early?
Temperature drives the clock. An incubator running at 99°F instead of 99.5°F can push hatch a full day late. Higher than 100°F pulls it forward but increases mortality and deformities. If hatch hasn't started by day 22, give it another 24 hours before opening anything.
How long should I leave hatched chicks in the incubator?
Up to 24 hours. They absorb the yolk sac just before hatching and don't need food or water for that period. Resist the urge to grab them the moment they fluff up - opening the incubator can ruin the hatch for any chick still working on the shell.