Incubation

The 7 common incubation mistakes (and how to avoid them)

Published 19 July 2026 · updated 21 July 2026 · 7-minute read

Dural's advice · from the ebook “From Egg to Hen”

A reliable incubator does half the work. The other half is what you do over 21 days. The good news is that failed hatches almost always come down to a handful of well-known reasons, every one of them avoidable. We see them come up every week at customer support, often in the same order.

The essentials in thirty seconds

Target temperature: 37.5 °C (99.5 °F) during incubation, 37.2 °C (99.0 °F) for the last three days.
Humidity: 45 to 55% up to day 18, then 65 to 75% for hatching.
Don't open the incubator more than once a day, and not at all after day 18.
Never help a chick out of its shell.
Keep the air vents open at all times.

Timeline of the 21 days of incubating a hen's egg, from day one to hatching — The 21 days of a hen's hatch. Day 18 marks the switch to lockdown: it's the pivotal moment of the whole cycle.

Setting the incubator up in an unstable room

An incubator holds 37.5 °C (99.5 °F), but it does so far more easily when its surroundings are steady. In a cold garage, a sun-baked conservatory or a room that swings from 12 to 25 °C (54 to 77 °F) over the day, it fights constantly and the inside temperature drifts. And it's those swings, more than the absolute figure, that wear the embryo down.

What to do: a steady room, ideally between 18 and 20 °C (64 to 68 °F), out of direct sun and draughts. Stand the incubator on a firm surface, more than 50 cm off the floor. It's the first thing our support team suggests, and often the only one needed.

Opening the lid too often

It's tempting to check on your eggs, especially the first time round. But every time you open the lid, temperature and humidity drop at once, and it then takes long minutes to bring them back. A broody hen, by contrast, only leaves her nest for ten to twenty minutes a day.

What to do: open it once a day at most during incubation, and not at all after day 18. If you need to top up the water, do it through the external filling ports made for that, with the lid closed.

Blocking the air vents

Many beginners close the vents to hold in humidity. It's exactly the wrong move: the embryo breathes through the roughly ten thousand pores in its shell and uses oxygen constantly, more and more as it grows. A poorly ventilated incubator slowly suffocates the clutch.

What to do: leave the vents open from the first day to the last. To adjust the humidity, change the water, never the ventilation. Your real guide is the air cell: visible when you candle, it takes up about a tenth of the egg at the start and a third by the end of incubation. Too small, and the air is too humid. Too large, and it's too dry.

Getting the humidity wrong

It's the number-one question our support team gets, and it almost always comes from too much water. Too much early on stops the air cell forming and leaves the chick no room to turn. Too little, and the membrane dries and hardens: the chick stays stuck inside, unable to finish hatching.

Phase	Temperature	Humidity	Turning
D1 to D18 · incubation	37.5 °C (99.5 °F)	45 to 55%	On
D18 to D21 · hatching	37.2 °C (99.0 °F)	65 to 75%	Off

→ Swipe the table to see all the columns.

What to do: lukewarm water, never cold, and the number of tanks or bottles your model's manual specifies. If humidity runs too high, open the vent valve before cutting the water. These figures are for hens: they rise noticeably for ducks and geese.

Candling too early, or for too long

Before the sixth or seventh day there is simply nothing to see: the embryo is still too small to read. Candling on day 3 tells you nothing and chills the eggs for no reason. At the other extreme, a candling session that drags on, eggs taken out and handled one by one for twenty minutes, does more harm than it yields information.

Candling comparison between an infertile egg that stays clear and a fertile egg showing a star of blood vessels — By the eighth day the difference is obvious: a web of vessels radiating from a dark spot on one side, an even transparency on the other.

What to do: first candling around the eighth day, five minutes at most for the whole clutch, clean hands. Remove the clear eggs, which could spoil and contaminate the rest. A second candling around the fourteenth day is useful but optional.

Helping a chick out

This is the most common mistake, and by far the hardest to resist. Watching a chick struggle for hours is hard to bear, and the urge to step in comes from the right place. But a chick normally takes up to twelve hours to break out of its shell, and all that time it is still drawing in the blood vessels that connect it to its membrane. Opening the shell for it causes a haemorrhage that is usually fatal.

What to do: nothing. Watch, don't touch, and don't open the incubator to lift out the first to hatch. Chicks can stay in the incubator for twenty-four hours without food or water: they live on the yolk they have just absorbed.

Skipping hygiene between hatches

A warm, damp incubator is a perfect breeding ground. Residue from one hatch contaminates the next, and the hatch rate collapses for no obvious reason, cycle after cycle.

What to do: before each cycle, wash the parts in warm water with a mild soap, disinfect with white vinegar diluted by half, never neat bleach, dry completely, then run it empty to settle. After a hatch, leave the incubator open for twenty-four hours before the full clean.

The mistake before all the others: choosing the wrong eggs

No setting can rescue an egg that should never have gone into the incubator in the first place. A hatching egg is less than ten days old, ideally between three and seven, has been stored point-down at 12 to 15 °C (54 to 59 °F), and has never been washed: the shell's natural protective film is what keeps bacteria out.

Grid of the nine egg defects to reject before incubation: elongated, calcified, pinholed, misshapen, hairline-cracked, soiled, round, mottled, wrinkled — Nine defects that doom an egg before day one. Weed them out when you set the eggs, and you'll spare yourself a disappointing candling on the eighth day.

One last reminder that saves a lot of disappointment: one incubator, one species at a time. Incubation times and settings differ too much from one species to another to run them side by side.

The takeaways

The mistake	The right habit
Cold or sunny room	Steady room, 18 to 20 °C (64 to 68 °F)
Opening it repeatedly	Once a day, none after D18
Vents closed	Open at all times
Humidity by guesswork	45 to 55%, then 65 to 75%
Candling on D3	First candling on D8, five minutes
Helping at hatching	Never step in
Incubator left uncleaned	Wash and disinfect before every cycle

None of these mistakes is disastrous on its own. It's their build-up that makes the difference between a disappointing hatch and a successful one. Avoid them, and a first hatch usually goes well.

To go further, our incubation guide walks through every stage day by day, and the timeline calculator gives you your candling, lockdown and hatching dates from the day you set the eggs.

Work out my incubation dates See our incubators