Hatching day by day: what happens, and what you do, across 21 days

Every number in that paragraph is published by Mississippi State University Extension, in publication P1182. They do not vary by brand, by breed or by opinion. What follows is the same figures laid out in the order you will meet them, plus the one thing the publications assume you already know and first-timers reliably do not.

Before day 1: the eggs

Hatchability is decided before the incubator is switched on. P1182 publishes the storage conditions: keep hatching eggs “in a cool, humid room,” with the best storage “near 60 F.” It also publishes the decay curve, which is the part worth knowing — hatchability falls with storage time, and “after 3 weeks of storage, the hatchability is near 0 percent.”

The practical version: set eggs within about a week of collection, ten days at the outside. A refrigerator is too cold, a warm kitchen counter is too warm, and an unheated spare room in spring is usually about right. Do not wash them. The egg handling page covers why the bloom on a shell matters.

The whole 21 days in one table

The half-degree disagreement, and what to do about it

Mississippi State Extension publishes 100 F for forced-air incubators. Brinsea ships every machine factory-preset to 99.5 F. Both figures are published by credible sources and the gap is half a degree.

The honest answer is that this half-degree is smaller than the difference between where your sensor sits and where the eggs sit. A thermometer at the top of a dome reads differently from one lying between the eggs, and both read differently from the inside of an egg. Leave the machine at its factory setting, put an independent thermometer at egg level, and worry about a two-degree drift rather than a half-degree calibration argument.

The still-air figure is the one not to fudge: P1182 publishes 102 F for a still-air incubator against 100 F forced-air, because without a fan the air stratifies and the reading at the top of the eggs is warmer than the air below. If your machine has no fan, the higher number is not an error.

Candling: two checks, not one

Candling is holding a bright focused light against the shell to see what is inside. P1182 publishes two checks: the first “after 4-7 days of incubation” and the second “after 14-16 days.” Doing only one is the commonest shortcut and it costs you twice.

The first check finds clears — infertile eggs, which never started. There is nothing wrong with them; fertility in a backyard flock is rarely total. Removing them matters because an unfertilized egg held at 100 F for three weeks can spoil and, in the worst case, burst, which contaminates the machine and the hatch.

The second check finds quitters — eggs that started and stopped. Same reasoning, later in the process, and it also tells you how many chicks to expect so day 21 is not a disappointment measured against the number you set.

Do both quickly and in a warm room. Every minute the egg is out of the incubator is a cooling minute, and the Brinsea machines actually publish a periodic egg-cooling feature on the basis that brief cooling is normal — a broody hen leaves the nest daily.

Day 18: lockdown, and the rule people break

Day 18 is the single most important day of the process and it consists mostly of things you stop doing.

Stop turning. P1182 is unambiguous: “DO NOT turn eggs during the 3 days before hatching.” A chick positions itself in the shell to pip, and turning it after that point can leave it unable to get out. If your machine has an automatic stop, confirm which day it triggers — the machines compared on this site stop two or three days out and one publishes no stop at all, so they are not interchangeable on this point.

Raise humidity to 65 percent or more, which P1182 gives as 89 to 90 F wet bulb. Open the vents further; the same publication notes air vents “should be almost fully open during the latter stages of hatching,” because a hatching chick is breathing air rather than diffusing oxygen through a shell.

Then close the lid and leave it closed. Every time you open an incubator during lockdown, humidity falls sharply and the membrane inside the shell can dry onto the chick. That is the mechanism behind “shrink-wrapping,” and it is the reason experienced hatchers are so insistent about a rule that sounds like superstition. Twenty-one days of patience is undone by curiosity on day 20.

Day 21 and after

Leave hatched chicks in the incubator until they are dry and fluffy. They can go 24 hours or more without food or water after hatching, on the yolk they absorbed, so there is no rush and opening the lid to remove one wet chick risks the eggs still hatching.

Once dry, they move to the brooder — and the brooder needs to have been running and up to temperature before that moment, not after. The published brooding schedule starts at 95 F at chick level under the heat source in week one, dropping about five degrees a week. That is the same figure whether the chick hatched in your kitchen or arrived in a box from a hatchery, and it is why setting the brooder up belongs on your day-18 list rather than your day-21 list.

Eggs that have not hatched by the end of day 21 occasionally hatch on day 22. After that, they are not going to. Do not keep a machine running for a week hoping.