If roosters live in the pen or on the farm with hens, it's nearly guaranteed that many of the eggs will be fertile. It's best to get fresh fertile eggs. You can collect fertile eggs for a few days and keep them in an egg carton for up to 2 weeks (not refrigerated or washed) IMPORTANT! In the storage, carton keep the eggs large end up small end down to keep the air sack open.
This is a fertile egg. Notice the "bulls-eye"
When not incubating eggs and you are storing them it's best to keep the eggs in a carton and "tilt" the carton each day from side to side or end to end. This will ensure that the embryo does not stick to the shell until you are ready to incubate the eggs.
This egg will not hatch. It is nonviable.
It's best to destroy all eggs that are not hatchable to prevent any breakage in your incubator and the spread of bacteria that will kill the other growing embryos
See in this photo is an "egg candling". This is where you carefully pick up eggs to check for embryos. Shine a very bright light through the egg shell to look for a developing baby chick. If you do not have an egg that looks like this in about a week. Its best to discard non fertile eggs.
Watch and actual egg to chick development
Pip day or "egg crack day" will be about day 18 or 19 or so in the incubation and you can hear the baby chicks peeping to get out. It's very tempting to open the incubator or to want to help the baby chick. Do NOT open the incubator, if you do the chicks will die from lack of humidity as the eggs will wrap tightly around the un-hatched chicks re-sealing them in the eggs. Let Mother Nature do the work of bringing life in the world. Wait until all chicks hatch (about day 22 or day 23. If any eggs are "late hatches" they will be usually weak or deformed. Its best to not allow these eggs to hatch as the chicks will be weak or deformed. They will rarely live past a few hours.
Ordering fertile eggs from the mail is really NOT a good idea. No matter HOW MANY people say it works well. Most of the time hatching eggs that have been wrapped well, even in 15 layers of bubble wrap, will be dropped kicked through the US postal system or zapped from many radiation or x-ray machines or handled roughly have a less than good chance of hatching without problems. The point is: you might not have a good hatch. There are cases where eggs will hatch but this is usually not the case. Most of the time people just want to sell eggs. Read the disclaimer and the fine print from the egg sellers that state the eggs will arrive safe and sound. It says: "we are not responsible for non hatching" so no refunds.
In most cases for the best hatches on fertile eggs, use your own chicken eggs or go and collect them from somewhere that you can drive to pick up fertile eggs.
We do buy fertile eggs from tested and regular growers and suppliers of many breeds. We keep our flocks varied and by having many breeds of chickens to select from each and every batch
Watch Broody Hen Hatch a Clutch of Eggs