Ask ten people why a hatch went badly and nine will answer temperature. It is the parameter everyone watches, which is exactly why it is rarely the one that failed. The disappointing hatches we get asked about are far more often a moisture problem, a storage problem, or a setting that was never uniform to begin with. Temperature just gets the blame because it is the number on the display.
Key takeaways
- Weight loss is the only measurement that tells you whether your humidity setting is right for your eggs, your altitude and your machine.
- A deviation of half a degree is enough to affect hatch results, which makes thermometer verification more useful than thermostat adjustment.
- Turning stops at day 18. Humidity goes up at the same moment, and the incubator stays shut from then on.
- Most of what determines a hatch happens before the eggs are set: fertility, storage and egg selection.
Before setting: the part that decides the rest
What happens before setting decides more of the outcome than anything you do afterwards. An incubator cannot improve an egg. It can only fail to damage it. Select eggs of even shape and shell quality, discard cracked, misshapen and heavily soiled ones, and do not wash away the cuticle in an effort to clean a dirty shell, because that removes the natural barrier protecting the embryo.
Storage is the variable most often mishandled. Hatching eggs held too long, or held at fluctuating temperature, lose hatchability in a way that no incubation profile recovers. Bring eggs to room temperature before setting so that condensation does not form on the shell, and run the machine empty for a day or two beforehand to confirm it actually holds the conditions its display claims. Fertility, of course, is decided further upstream still, in the breeding flock, a subject we treat separately in our guide to the basics of poultry reproduction for successful incubation.
The four parameters and what each one actually controls
Each parameter controls a distinct biological process, which is why they cannot be traded against each other. Temperature drives the rate of embryonic development. Humidity governs how much water the egg loses through the shell. Turning prevents the embryo adhering to the shell membrane and supports the development of the extra-embryonic membranes. Air exchange supplies oxygen and removes the carbon dioxide the embryo produces in increasing quantity as it grows.
| Phase | Temperature | Relative humidity | Turning |
|---|---|---|---|
| Setting, days 1 to 17 | 37.5 to 37.8 °C (99.5 to 100 °F), held steady | Around 45 to 55 per cent, adjusted to hit the weight loss target | At least 4 to 6 times per day, automatic or manual |
| Transfer, day 18 | Same setting, minimise the time eggs spend out of the machine | Weigh here: cumulative loss should be about 11 to 13 per cent | Stops |
| Hatching, days 18 to 21 | Unchanged unless your equipment guide specifies otherwise | Raised to roughly 65 to 70 per cent | None, and the machine stays closed |
Those figures are the commonly cited working range for chicken eggs. Duck, quail and turkey eggs run to different incubation lengths and different profiles, so check the values for the species you are actually setting rather than transposing the chicken numbers.
Why weight loss beats the humidity reading
Weight loss is the measurement that makes humidity meaningful. A hygrometer tells you the condition of the air in the machine. It does not tell you how a specific batch of eggs, with a specific shell porosity, at your altitude, is responding to that air. Humidity should be monitored and adjusted so that the eggs lose about 11 to 13 per cent of their initial weight by day 18, and that target is what you steer towards rather than a fixed percentage on a dial.
The method is unglamorous and takes ten minutes. Weigh a tray of eggs at setting, weigh the same tray at day 7 and again at day 14, and compare the trajectory against a straight line to the target. Losing too little means humidity is too high, and the air cell will be too small for the chick to draw its first breath comfortably. Losing too much means the reverse, and the chick risks becoming stuck in a membrane that has dried around it.
Temperature: verify the instrument, not the thermostat
Temperature errors are usually measurement errors. A deviation of only half a degree is enough to affect hatching outcomes and energy consumption, which means the accuracy of your thermometer matters at least as much as the precision of your controller. A controller holding a wrong reading perfectly will produce a consistently poor hatch and give you no signal at all.
Check the reading against an independent, verified thermometer placed at egg level, not at the top of the cabinet where the sensor usually sits. In still-air machines the gradient between the top and the bottom of the chamber can be considerable. Forced-air machines even that out, which is one practical reason they hold larger settings more reliably.
Turning, and why it stops on day 18
Turning until day 18 is recommended, at least four to six times a day, so that development stays uniform and the embryo does not adhere to the shell membrane. An odd number of turns per day is the traditional refinement, so that eggs do not spend every night in the same orientation. If you are turning by hand, a pencil mark on one side is still the simplest way to know what has been done.
Turning stops at day 18 because the embryo is moving into hatching position, head under the right wing, and further movement interferes with it. That same moment is when eggs move to the hatcher, humidity goes up, and the machine stays shut. In commercial hatcheries this transfer point is also when in ovo vaccination is carried out, on day 18 to 19 of incubation, which is not a coincidence: it is the one window where the embryo is developed enough to be reached safely and not yet hatching.
Candling: what it can and cannot resolve
Candling separates fertile from infertile eggs and identifies early embryonic death, and the timing determines how reliable that separation is. Around 9 to 12 days of incubation the two are easiest to distinguish, which is why commercial operations candle in that window rather than earlier. Candle at day 5 and you will book early dead embryos as infertile eggs, which points your investigation at the breeding flock when the problem may well be in your own machine.
What candling cannot do is tell you why. It gives you a count and a stage, and the interpretation comes from combining that count with your incubation records and, at the end, with what you find when you break out the eggs that did not hatch.
Hatch day, and the temptation to help
Hatch day is mostly an exercise in not intervening. Chicks pip internally into the air cell, then externally through the shell, and the process can legitimately take many hours. Opening the machine during that period drops the humidity that the chick depends on to free itself, and the membrane can dry around it.
Resist the urge to assist a struggling chick unless you have a specific reason and know what you are doing. A chick that cannot get out on its own often cannot for a reason, and helping it out may simply postpone the outcome. Once hatched and dry, chicks move to a brooder with a heat source, clean water and a starter feed. Everything they need in the first days is set up before the first one hatches, not during.
The five mistakes that cost the most
- Steering humidity by the dial instead of by weight loss. The most common cause of chicks that pip and then fail to hatch.
- Trusting an unverified thermometer. Half a degree of error, held perfectly, ruins a hatch quietly and repeatedly.
- Candling too early. It misattributes your losses and sends you looking in the wrong place.
- Opening the machine after day 18. Every opening costs humidity at the moment it matters most.
- Setting eggs that were never going to hatch. Poor storage, cracked shells and washed cuticles are decided before day one.
Questions we hear most often
Why did my chicks pip and then die in the shell?
The classic pattern points at moisture management and at conditions during the hatching phase. Insufficient weight loss over the setting period leaves an air cell too small, and low humidity during hatching lets the membrane dry around a chick that has already broken through. Weigh a tray next time and you will usually find the answer before day 18 rather than after day 21.
Is an automatic turner worth the cost?
For anything beyond a very small setting, yes, mainly because it removes the failure mode of a turn that did not happen. Manual turning works perfectly well when it is actually done four to six times a day, every day, which is a harder commitment than it looks over three weeks.
Does still air or forced air make a real difference?
It changes how much you can trust a single temperature reading. Still-air machines develop a vertical gradient, so the value at egg level differs from the value at the sensor. Forced-air machines circulate and even that out, which is why their published set points and still-air set points are not interchangeable.
Can I set eggs from different species together?
Not usefully. Incubation length, temperature preference and humidity profile differ by species, and a shared machine forces a compromise that is wrong for both. Different setting dates in the same machine cause a similar problem, since the transfer point for one batch means opening the machine during another batch’s hatching phase.
Before the incubator, the breeding flock
No incubation profile compensates for low fertility. If your hatch of set is disappointing but hatch of fertile looks normal, the problem is upstream of the machine entirely.
Go back to the reproduction fundamentals behind a good hatch
Sources: E+E Elektronik technical note on incubation temperature for poultry (2025); The Poultry Site, Breakout Analyses Guide for Hatcheries; Royal Pas Reform, In-ovo vaccination requires good hatchery management. Consulted August 2026. Parameter ranges given here are for chicken eggs; confirm the values for your species and your equipment against the manufacturer’s guide.