What can honestly be known at hatch
Very little, for most keepers. The accurate method at day-old — vent sexing, reading tiny anatomy inside the vent — takes years of training and is how hatcheries sort commercial chicks; it is not a skill to improvise on your own birds, and squeezing chicks to try can injure them. Two genuine exceptions exist. Sex-linked crosses are bred so males and females hatch in different down colours or patterns, and autosexing pure breeds carry the same trick in their markings, so a chick of those types can be sexed on sight by anyone who knows the breed's key. Feather sexing — comparing the wing feather rows of day-old chicks — works only in specific crosses bred from fast- and slow-feathering lines; applied to ordinary breeds it produces confident, wrong answers.
The clues that build from four to eight weeks
From about a month old, differences start accumulating rather than appearing. In most breeds the cockerels' combs grow larger and pink up earlier than their sisters', and small wattles show sooner; pullets' combs stay small and pale until much nearer laying. Cockerels often stand taller on thicker legs, watch the world with a bolder, more upright posture, and spar chest-to-chest with their brothers, while pullets feather out smoothly and get on with feeding. Treat every one of these as a leaning, not a verdict: a fast-developing pullet of a large-combed breed outsprints a slow cockerel of another line, and mixed-breed youngsters scramble the signals further. Keep loose notes bird by bird — the earliest comb, the boldest stance — because the pattern across weeks is worth more than any single observation.
The three-month certainties
By around twelve weeks the plumage gives the answer away. Cockerels grow pointed, glossy hackle feathers around the neck and long, pointed saddle feathers that drape in front of the tail, plus the first curved sickle feathers in the tail itself; pullets carry rounded hackles and saddles that blend into the body. Practise crowing usually starts somewhere in this window too, thin and ridiculous at first, and settles any remaining doubt in that direction. In the other direction, the first egg — typically somewhere around five to six months depending on breed and season — is the pullet's own final confirmation. By this stage your earlier notes should have narrowed most birds down, with the plumage confirming or overturning them.
Why the record matters as much as the answer
Sexing is not trivia: roosters change what a keeper may legally keep in many neighbourhoods, how many hens a flock needs, and whether fertile eggs and future chicks are part of the plan. A bird misrecorded for months scrambles breeding groups, sales and rehoming decisions, so update each youngster's record at the moment its signs firm up rather than relying on memory at sorting time. Note the distinguishing marks you used — leg ring colour, feather pattern, position in the hatch — so the bird you sexed is the bird you think it is.
Accept the margin of error, and plan around it
Even experienced keepers misread a proportion of youngsters, especially slow-maturing cockerels of heavy breeds and fast pullets of light ones. Buy or hatch with a cockerel contingency already decided — a keeper who will take him, a separate bachelor setup, or a firm plan of your own — so a surprise rooster is a logistics problem rather than a crisis. Any youngster that is off its feed, injured or unwell should be checked by a vet on its own merits; illness is not a sexing clue, and a quiet, hunched bird is a health question, not a shy pullet.
Once a bird's sex is settled, its identity is settled too — and a KinsLe Pet Pass holds that verified identity for each chicken, so every bird in the flock carries an accurate record wherever it goes.