Guide To Hatch Chicken Eggs in 21 Days.

General Hints 

First things first - eggs should hatch in 21 days, though some may hatch a day or 2 early and some a day or 2 late, after the incubation period began. A "day" is counted as a full 24 hours, so Day 1 would be the first 24 after setting the egg, Day 2 the next 24 hours etc. If you set eggs on a Monday, it's usually a safe bet that they will hatch on a Monday, 3 weeks later.

Select clean, even shaped, undamaged eggs for incubating. If possible, do not store them too long pre-incubation. Ideally eggs should be set within a week after being laid and after 10 days the hatchability of the eggs drops significantly.

**A note on shipped eggs: Shipped eggs should be allowed to rest and for 24 hours prior to setting, to allow the contents of the eggs to settle. Place shipped eggs upright, with the fat end of the egg up, in an egg carton, or something similar. Shipped eggs often have loose or damaged air cells. For more info and tips on managing these see here. 

Before putting your eggs into an incubator, plug it in and make sure the temperature is steady. In a forced air incubator (with a fan) the temperature should be 99-99.5*F. In a still air incubator the temperature should be slightly higher, 101-102*F measured at the top of the eggs.  I use a thermometer and a hygrometer (which measures humidity) in my incubator. Hygrometers can be purchased quite cheaply at a cigar shop, Radio Shack and I believe even Walmart. You want 45-50% humidity for day 1-18, then 65% for the last few days.

Use a non-toxic marker and mark eggs with an X on one side and an O on the other, so when you are turning them you can make sure they all got turned. More about turning later... 

Incubators

There are many makes and models of incubators for sale and they vary greatly in price, quality and user-friendliness.

Fertility and Candling 

Natural fertility is rarely 100% - it may vary from 55% to 95% with season, condition and type of birds. You might be safe to expect that 50% to 75% of the fertile eggs will hatch, though 90%-100% hatches can and does happen. With shipped eggs the hatch rate is approximately 50% overall. Fertility of eggs cannot be determined before incubating them. After 5-7 days, white-shelled eggs can be candled to see if embryos have developed.

The Air Bubble in the Egg

Soon after an egg is laid, a small air bubble forms in the large end under the shell. A membrane separating the mass of the egg and the air bubble moves back and forth to relieve stress and pressure on the embryo resulting from changes in temperature. The drier the outside air is, the more fluid is depleted and the faster the bubble grows. Correct humidity in the incubator insures that the bubble does not grow too big, depleting essential fluids, or deny the chick enough air by remaining too small.

The importance of correct humidity is more apparent at the end of incubation. The normal condition is that the air cell has enlarged to the point where the chick can reach his beak through the membrane wall, allowing it to breathe, before it pips through the shell, after which it will "zip" around the shell. If humidity has been excessive, the chick may pip internally into the air cell and drown in excess fluid. On the other hand, if humidity has been too low, the air cell will be oversized and the chick may be "shrink wrapped" in the inner membrane and unable to hatch.

Positioning of Eggs

An incubating egg could set in a normal position as it would on a flat surface; that is with the large end slightly higher than the point, or upright in egg cartons/turners, with the fat end of the egg always up. An egg that persistently has the small end elevated may cause the embryo to be misoriented with the head toward the small end. In the misoriented position, the chick is likely to drown on pipping. Therefore, it is quite important that in general, the large end of eggs should be slightly higher than the small ends; or as they would lie naturally on a flat surface.

Turning

Turning is essential during the first 14 days of incubation and should be continued until 3 days prior to the eggs expected hatch day. If hand turning, always turn the eggs an uneven number of times a day, so the eggs do not spent two nights in a row in the same position. If not turned to a fresh position frequently during the early stages, the developing embryo touches the shell membrane and sticks to it causing abnormal growth. Turning the egg aids these movements within the egg, and mimics what a mother hen would do naturally.

What to do With Hatched Chickens

After the chick hatched allow it to dry off and fluff up in the incubator before removing it to a brooder. Newly hatched chicks can survive for up to 3 days on the yolk they absorb during the hatching process, but once you put them in the brooder make sure there is at least water available and offer them food after a day or 2.

Feeding Baby Chicks

Feed and water must be available at all times from the time they are out of the incubator. Do not dole out a measured daily ration. Do not let feed or water run out! Chicks need to be fed a chick starter. Medicated chick starter can be fed to help prevent Coccidiosis. Please note: chicks fed a medicated starter may still get coccidiosis. The medicine in the feed only help prevent it.

Prevent Drowning 

Water receptacles are a problem with baby birds during their first week. Chicks are clumsy and can easily fall into water dishes and drown. A common device to prevent drowning is to use a shallow water cup with marbles set in the water over the entire drinking area. The chicks will drink in the spaces between the marbles.