American hens laid about 105 billion eggs in the year ending November 30, 2025. Of those, 15.2 billion were hatching eggs, the ones sent to incubators to become chicks. Call it one egg in seven.
The other six came from hens that have never been near a rooster.
I order chicks from a hatchery like everybody else, and it is easy. It is also not the same thing as a backyard flock making its own. If you want that, or if you just cracked an egg and found a small pale bullseye sitting on the yolk, here is what is happening inside the bird.
How do chicken eggs get fertilized?
A chicken egg is fertilized inside the hen, in the first few inches of her oviduct, before the shell or the white exists.
Mating comes first. The rooster transfers sperm through brief contact, and those sperm get stored in glands along her oviduct that hold more than half a million at a time. Nothing has to happen again for days.
Then the hen ovulates. A mature yolk leaves her ovary and within 20 minutes it is caught by the infundibulum, the funnel at the top of the oviduct. Sperm leave the storage glands and swim up to meet it there. Around 30 of them have to reach the germinal disc, the pale spot on the yolk’s surface, to give that egg a 95 percent chance of being fertilized.
About fifteen minutes later the yolk moves on down the tube, fertilized or not.
That is the whole window. Everything after it is assembly. The white goes on in the magnum, the membranes in the isthmus, the shell in the uterus, and the finished egg takes about 25 hours to build.
Sperm never touch a shell. By the time there is a shell, the question was settled almost a day earlier.
How do chickens mate?
With a dance, and about three seconds of contact.
The rooster opens with a display called tidbitting. He picks up a scrap of food, drops it, picks it up again, and makes a fast clucking call over the top of it. In a video playback study of 24 bantam hens, birds shown the movement with no sound searched for food more than under any other condition tested. A lab, not a pasture, but the finding is clean. The moving beak carries the message on its own.
If she is interested, she crouches and spreads her wings a little. If he is pushy, or short on hens to choose from, he skips the negotiation entirely. He mounts, grips the feathers at the back of her neck to steady himself, and the two press their cloacas together. That is the transfer, and it is over in seconds.
I have kept laying hens for years, and it looks far rougher than it is.
Roosters have no penis. Their two testes sit internally, on either side of the backbone inside the abdominal cavity, and a mature rooster produces roughly 35,000 sperm every second of his life. Not every mating. Every second!
Do chickens need a rooster to lay eggs?
No. A hen ovulates on her own schedule whether or not a male exists.
A rooster changes what is inside the egg, not whether there is one. The USDA says most eggs sold are infertile for the simple reason that roosters are not housed with commercial laying hens. There is nothing in the barn to fertilize anything.
How long after mating does a hen lay a fertile egg?
Much faster than most of the internet will tell you.
Mississippi State’s poultry extension service puts a number on it. Drop a sexually active rooster into a flock and fertile eggs by the second day are normal, because if a hen mates and ovulates soon after, that next yolk can be fertilized. The minimum from mating to a hatchable egg is 30 to 36 hours. Across a whole flock, allow four to seven days before fertility runs high, since one rooster needs time to get around to everybody.
The figure repeated on chicken blogs is ten to fourteen days. It is wrong, and almost nobody repeating it made it up. It got copied from one post into the next until it looked like agreement, which is what happens to a number nobody walks back up to its source.
The back end of the window is longer than the front. A hen’s fertility peaks for three or four days after a single mating and then tapers, though sperm can stay alive in her storage glands for up to three weeks. Pull the rooster out and hens can go on laying fertile eggs for four weeks.
How can you tell if an egg is fertilized?
Two methods work, and the one most people reach for first does not.
Crack it open and look at the yolk. An unfertilized egg carries a small white dot called the blastodisc, about half the size of a pencil eraser. A fertilized one carries a blastoderm, the same spot with a faint ring around it, like a tiny bullseye. That ring is the entire visible difference.
Candle it, once incubation has started. Work in a dark room with a narrow beam held against the wide end of the egg. Mississippi State recommends testing after four days and up to seven. A live embryo looks spider-like, a dark body with blood vessels running out from it like legs. Clear with nothing but a yolk shadow means it was never fertile. A dark ring means it started and quit.
The float test does not answer this question. Drop an egg in water and what you learn is how big the air cell is. The air cell grows as moisture escapes through the shell, so a floater is an old egg. Old, not fertile. Two different questions, and the test only answers one.
Keep that last one as a habit. Before you trust any test, ask what it was built to measure.
Fertilization is a tell, not a trait
A fertilized egg is not a better egg. The USDA is flat about it: no nutritional difference between fertilized and infertile eggs, and no benefit to eating one.
You also will not find one in a supermarket if you go hunting. Graded eggs get candled, and any egg showing cell development is pulled before it reaches a carton.
Which is what makes fertility useful. It is not a property of the food. It is information about the operation. A fertile egg means a flock small enough to keep a rooster in it, which means birds that were not stacked in a house of 300,000, which usually means a different feed, more room, and a farmer who could pick those hens out of a crowd.
None of that comes from the sperm. All of it comes from the same conditions that allowed the sperm to be there. Fertilization does not improve an egg. It tells on the farm that produced it.
What is inside a fertilized egg
A live embryo, and more of one than most people expect.
By the time a hen lays a fertilized egg, the embryo has been developing for about 25 hours and has divided into roughly 20,000 cells. Then it stops. Development pauses once the egg cools below body temperature and stays paused until something warms it up again, which is why a fertile egg in your kitchen never becomes anything.
That is the argument for collecting daily. An egg pulled from under a broody hen who has been sitting a week is a different object than one gathered this morning, and you will know it the second you crack it.
How to get better eggs
The useful advice has almost nothing to do with fertility, since you cannot buy a fertilized egg anyway. It has to do with the conditions fertility signals.
Ask one question. When you buy eggs from a person instead of a shelf, ask what the birds eat. It costs nothing, it takes ten seconds, and the answer tells you more than any carton will.
Buy from a flock you could go look at. A neighbor’s birds, a coworker drowning in eggs, a market stand where the farmer can tell you where the coop sits. Local beats every label here, every time.
In a store, go pasture-raised with a real humane certification. Best carton on a supermarket shelf, and it is not close. Vegetarian-fed is the worst, and the reason is sitting right there in the name.
If you want your own, start with three hens and no rooster. You get eggs in a few months without the crowing or the neighbors. Add a rooster later, when you actually want chicks.
If you keep chickens and you want chicks, put a rooster in with the flock, give it a week, and start candling four days into incubation.
If you never wanted chicks, you have not been missing anything, and neither have your eggs.
Either way, the thing worth chasing was never fertility. Go ask somebody what their birds eat, and buy from whoever gives you the best answer.
