Candling Eggs: Day 7, 14, and 18 Checks
TL;DR: Candling means holding a bright light behind an egg to see inside without opening it, done at day 7, 14, and 18 of the 21-day incubation cycle. A fertile egg shows branching blood vessels by day 7, fills in dark with a visible air cell by day 14, and shows a large defined air cell with almost no light passing through by day 18. Clear eggs are infertile; a blood ring or stalled growth marks a quitter.
What Is Candling and Why Does It Matter?
Candling is the practice of holding a bright light source behind or under an egg, usually in a dark room, so the shadows of what’s developing inside become visible through the shell without cracking it open. It’s the only practical way to check on a developing embryo mid-incubation, and doing it at the right points in the 21-day cycle tells you which eggs are worth the incubator space and which aren’t.
This matters most before lockdown (day 19), because that’s your last real opportunity to remove eggs that aren’t developing before the incubator closes up for the final stretch. See our full incubation guide for how candling fits into the whole 21-day process — this article goes deep on candling specifically.
What Do You Need to Candle an Egg?
A bright, concentrated light source and a dark room are all you actually need — a dedicated egg candler works well, but a strong flashlight or phone light held close against the shell in a dark room does the job for a small backyard batch. Cup the light against the wide end of the egg (where the air cell sits) and look at what shows through from the side or the pointed end.
Work quickly and gently. Eggs cool and lose humidity every minute they’re out of the incubator, so a candling session should take a few seconds per egg, not a leisurely inspection — get the read and put the egg back.
What Does Day 7 Candling Show?
At day 7, a fertile, developing egg shows a small dark spot with fine blood vessels branching outward from it, an appearance often described as looking like a spider. This is the earliest reliable candling checkpoint — trying to candle much earlier than day 7 usually shows too little to make a confident call either way.
| Egg type at day 7 | What you see |
|---|---|
| Fertile, developing | Dark spot with branching blood vessels (“spider” pattern) |
| Infertile | Clear, no blood vessels, looks essentially unchanged from day 1 |
| Early quitter | Blood ring — a reddish ring visible inside the shell — or vessels that look faint and stalled |
A clear egg at day 7 with no visible vessels is most likely infertile. Some keepers wait until day 10 for a second look on borderline eggs before making a final call, since very early development can be genuinely hard to read.
What Does Day 14 Candling Show?
By day 14, a healthy developing egg looks mostly dark and filled in when candled, with a clear space only at the wide end — that’s the air cell, which grows steadily through incubation as the egg loses moisture. You may catch movement if you watch for a moment and the embryo shifts position inside.
This is usually the easiest checkpoint to read with confidence, because the difference between a developing egg (dark, filled, defined air cell) and a problem egg (still largely clear, or showing a blood ring) is much more obvious than it was at day 7.
What Does Day 18 Candling Show?
At day 18, the last check before lockdown, a healthy egg shows a large, clearly defined air cell at the wide end and very little light passing through the rest of the shell, since the chick now fills most of the internal space. This is your final opportunity to pull non-developing eggs before turning stops and lockdown begins.
| Checkpoint | What a healthy egg shows | What a problem egg shows |
|---|---|---|
| Day 7 | Blood vessels branching from a dark spot | Clear (infertile) or a blood ring (early quitter) |
| Day 14 | Mostly dark, filled in, defined air cell, possible movement | Still largely clear, or stalled/reduced from day 7 |
| Day 18 | Large defined air cell, minimal light through the rest of the shell | Underdeveloped air cell, or egg still translucent |
What Does an Infertile Egg Look Like?
An infertile egg stays clear and see-through at every candling checkpoint, with no blood vessels, no dark mass, and light passing through freely, looking essentially the same at day 14 as it did on day 1. There’s nothing to see because nothing started developing — this is different from a quitter, which shows visible signs that something began and then stopped.
Infertile eggs are common in any batch and aren’t necessarily a sign of a problem with your incubator or your breeding stock — fertility rates vary for reasons well beyond incubation technique, including the age and condition of the breeding birds that produced the eggs.
What Is a Quitter Egg?
A quitter is an egg that was fertile and had started developing, then stopped partway through — it typically shows a blood ring (a reddish ring visible inside the shell, most obvious around day 7-10) or an embryo that looks the same size or smaller at a later candling than it did earlier, instead of continuing to grow. The distinction matters because a quitter had a working embryo at some point, unlike an infertile egg that never did.
A blood ring specifically usually means the embryo died in the first week. Later quitters, caught at day 14 or 18, show as an egg that looks underdeveloped for its day count rather than a clean blood ring. Either way, remove quitter eggs once you’re confident in the call — they won’t recover and progress, and they’re occupying space a developing egg could use.
What Do You Do With Eggs That Don’t Pass Candling?
Remove infertile and quitter eggs from the incubator once you’re confident in the read, typically by day 14 or 18 at the latest, both to free up space and because a spoiled egg occasionally affects the eggs around it. If you’re not sure on a borderline call, it’s reasonable to leave a questionable egg in until the next checkpoint rather than guess — a wrong call in either direction costs you either incubator space or a viable egg.
Once the eggs that are candling through cleanly reach lockdown, the process shifts from checking to leaving the incubator alone — see our incubation guide for what happens during those final 3 days, and our pillar guide on how to brood chicks for what comes after hatch.
The Honest Limits Here
Candling reads are a skill that improves with practice, and a beginner’s first few candling sessions will genuinely be harder to interpret confidently than an experienced breeder’s. Shell color and thickness also affect how much detail you can see — darker or thicker-shelled eggs are harder to candle clearly than pale, thin-shelled ones, regardless of how good your light source is. Treat an uncertain call as a reason to wait for the next checkpoint rather than a reason to guess.
Candling is one step inside the full 21-day cycle — see our how to incubate chicken eggs guide for temperature, humidity, turning, and lockdown, and our how to brood chicks pillar for what happens once eggs hatch.
Frequently Asked Questions
What is egg candling?
Candling is holding a bright light behind an egg in a dark room to see the shadows inside — blood vessels, the embryo, and the air cell — without opening the shell. It shows whether an egg is developing normally.
What do you see when you candle an egg at day 7?
A fertile, developing egg shows a web of fine blood vessels branching out from a small dark spot, sometimes called a spider. A clear, empty-looking egg at day 7 is most likely infertile.
What do you see when you candle an egg at day 14?
The egg should look mostly dark and filled in, with only the air cell showing as a clear space at the wide end. You may see movement if you watch closely and the embryo shifts.
What do you see when you candle an egg at day 18?
A near-full egg with a large, clearly defined air cell at the wide end, and very little light passing through the rest of the shell. This is the last check before lockdown.
What does an infertile egg look like when candled?
Clear and see-through with no blood vessels, no dark mass, and light passing through easily, looking essentially the same at day 7 as it did on day 1.
What is a quitter egg?
A quitter is an egg that was fertile and started developing, then stopped. It typically shows a blood ring — a reddish ring inside the shell — or an embryo that looks the same or smaller than it did at an earlier candling instead of larger.
Should you remove infertile or quitter eggs from the incubator?
Yes, remove them once you are confident in the call, usually by day 14 or 18 at the latest. A bad egg can occasionally spoil and affect nearby eggs, and it is taking up incubator space that could hold a developing one.
Can you candle eggs too often?
Yes — keep candling brief and infrequent. Each session outside the incubator cools the eggs and interrupts the stable temperature and humidity they need, so stick to the day 7, 14, and 18 checkpoints rather than checking daily.