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In a dark room, hold a bright LED light to each egg’s blunt end for about 5 seconds. On day 7, a fertile chicken egg shows a dark eye spot with spider-like veins, a clear egg is infertile, and a sharp red ring is a blood ring (early death). By day 14 live eggs look mostly dark. If unsure, leave it in and recheck in 3 days.
What you need to candle eggs
All you need is a dark room and a bright, narrow light. Candling works by shining light through the shell so you can see the shadow of the embryo, the veins and the air cell inside.
- A dark room. Candle at night or in a windowless bathroom. Even a little daylight makes early embryos hard to see.
- A bright LED candler. A dedicated candler has a rubber collar that seals against the shell, so no light leaks around the sides. Many incubators include one. A small, bright LED flashlight works too if you cup your fingers around the egg. LEDs also stay cool, unlike old incandescent bulbs.
- Clean, dry hands and a pencil. Mark each egg so you can track which ones you’re watching.
- A plan to be quick. Aim for about 5 seconds per egg and keep the whole session short. Eggs cool slowly and recover well from a brief check, but don’t leave the lid open while you work.
How to candle eggs step by step
1. Pick the right day
For chicken eggs, candle on day 7 and day 14. White eggs can be checked as early as day 4–5. An optional quick check on day 17 or 18 lets you remove dead eggs before lockdown. Our 21-day incubation calendar shows what the embryo should look like each day.
2. Darken the room and wash your hands
Let your eyes adjust for a minute. Clean, dry hands avoid passing bacteria and oils onto the porous shell.
3. Hold the light to the blunt end
Take one egg at a time. Press the candler against the blunt end, where the air cell sits, and tilt the egg slowly so the light passes through the middle. Don’t shake or spin the egg.
4. Look for three things
Look for an embryo or eye spot, a network of veins, and the air cell at the top. Movement is a bonus: a live embryo often jerks or twitches when the light hits it.
5. Mark and record
Pencil a simple code on each egg: a tick for fertile, a question mark for unsure, an X for clear. Draw a line along the air cell edge on day 14 and 18 to see how it grows.
6. Remove only what you’re sure about
Clear eggs, blood rings, cracked or leaking eggs and anything that smells come out. Everything else goes back in. If unsure, leave it in and recheck in 3 days. A slow developer looks very different after three days; a dead one doesn’t change.
Candling pictures: what eggs look like day by day
These illustrations show a chicken egg held blunt end up over a candler. Real eggs vary with shell color and thickness, but the patterns are the same.
Day 4–5: the spider
On white or pale shells, a fertile egg shows a small dark dot with thin red veins spreading from it, like a tiny spider. It’s easy to miss on brown eggs at this stage, so don’t remove anything this early unless it is clearly cracked or leaking.
Day 7: eye spot and veins
This is the most useful candling day. A fertile egg shows a dark eye spot inside a web of veins that reaches toward the shell. A clear egg glows evenly with only a faint shadow of the yolk. It was either infertile or died in the first day or two.
Day 10: a bigger dark mass
The embryo is a larger dark shape and the veins are thicker and run right to the shell. You may see it moving.
Day 14: mostly dark
A live egg is mostly dark, with light showing only near the narrow end and around the edges. The air cell at the blunt end has a crisp, defined line. Veins are often visible along that line.
Day 17–18: dark with a big air cell
The egg is almost completely dark. The air cell is large, and its lower edge often tilts or dips as the chick moves toward it. When you see a shadow pushing up into the air cell, that’s the internal pip: the beak has broken into the air cell and hatching is a day or so away.
What you see, what it means, what to do
| What you see | What it means | What to do |
|---|---|---|
| Dark spot + spider-like veins (day 4–7) | Fertile, developing | Keep incubating |
| Even glow, faint yolk shadow (day 7) | Infertile, or died in the first 1–2 days | Remove |
| Sharp red ring, no veins | Blood ring: embryo died early and blood pooled into a ring | Remove |
| Faint, blurry shadow, can’t tell | Slow starter, thick or dark shell, or early death | Leave it in; recheck in 3 days |
| Dark blob, no veins, no movement (day 10–14) | Quitter: died after starting to develop | Recheck once to confirm, then remove |
| Mostly dark, crisp air cell (day 14) | Healthy embryo | Keep incubating |
| Air cell much too small or too large | Humidity too high or too low | Adjust humidity; see the humidity guide |
| Wobbly or loose air cell | Damaged air cell, common in shipped eggs | Keep incubating; handle gently |
| Shadow pushing into air cell (day 19–20) | Internal pip | Lockdown: keep the lid shut |
| Hairline crack | Shell damage; risk of drying and bacteria | Seal with a thin dab of wax or glue if alive; otherwise remove |
| Bad smell, oozing, beads of moisture | Bacterial contamination | Remove at once |
Air cell size is the best free tool you have for judging humidity. The incubator humidity guide shows how big it should be on days 7, 14 and 18.
How to tell if an egg is fertile
The only way to tell before incubation is to crack an egg open. After 4–7 days in the incubator, candling tells you without breaking anything.
- Before incubating: crack one egg from the same batch. On the yolk, an infertile egg has a small, solid white dot. A fertile egg has a slightly larger white ring with a clear center, often called a “bullseye”.
- During incubation: veins by day 7 mean the egg was fertile. A clear egg on day 7 was usually infertile.
- After the hatch: open unhatched eggs (outdoors, at arm’s length). A blood ring or tiny embryo means it was fertile and died; nothing but yolk and white means it never started.
Supermarket eggs come from flocks without roosters and are nearly all infertile. See can you hatch store-bought eggs? for the details.
Blood rings, quitters and when to remove an egg
Remove an egg when you are certain it is dead or dangerous: clear on day 7 or later, a blood ring, a confirmed quitter, a crack that leaks, or any smell. When in doubt, wait. A dead egg left in for three more days does very little harm. A live egg thrown out is gone for good.
Blood rings
A blood ring forms when the embryo dies early and its blood vessels pull away from it, leaving a red circle around the yolk. Common causes are temperature swings, rough handling, or eggs stored too long or too warm before setting. Remove blood-ring eggs; they will not develop.
Quitters
A quitter is an egg that develops for a while and then stops. On candling it shows a dark mass with no clear veins and no movement, often with a hazy or dark ring. Recheck once before removing. Several quitters at the same stage point to a problem on that day, such as a temperature spike or power cut. See hatching troubleshooting for causes.
Cracked eggs
A fine hairline crack on a live egg can be sealed with a thin layer of unscented candle wax or non-toxic white glue. It lets moisture and bacteria in, so watch it closely. Remove eggs with large or leaking cracks.
The sniff test
Lift the lid and smell. A rotten egg smells of sulfur, and it may sweat beads of moisture or look darker than its neighbors. Remove it gently, without shaking, and take it straight outside.
Rotten eggs can burst. Gas builds up inside contaminated eggs, and a burst egg can spread bacteria to every other egg in the incubator. If an egg smells, oozes or looks wet, remove it right away and wipe the area clean.
How to candle dark, blue, duck and quail eggs
Dark, speckled and thick shells block light, so give them more time in the incubator before judging and use the brightest light you can.
- Dark brown eggs (Marans, Welsummer): wait until day 8–10 for a first check. Look for movement and the outline of a dark mass rather than fine veins.
- Blue and green eggs: the tinted shell turns the glow greenish but veins show about as well as on light brown eggs. Day 7 usually works.
- Duck eggs: they take 28 days, so check on about day 7–10 and again around day 14–18. Their thicker shells and larger size need a bright light. Muscovy eggs take 35 days. More in the duck egg incubation guide.
- Quail eggs: speckled shells make candling hard. A very bright, narrow light helps, and day 5–7 works best for Coturnix. Many keepers skip candling quail and simply wait for the hatch. See the quail incubation guide.
Can’t see anything in a dark egg? Compare it with a known clear egg from the same batch. A live egg looks darker and more blurred than a clear one, even when you can’t see veins.
Frequently asked questions
What does a fertile egg look like when candling on day 7?
A fertile chicken egg on day 7 shows a dark spot, the eye, near the middle, surrounded by red veins that spread out like a spider web. The embryo may twitch when the light hits it. An infertile egg glows evenly and shows only a faint yolk shadow with no veins.
What is a blood ring in an egg?
A blood ring is a sharp red circle you see when candling an egg whose embryo died early, usually in the first week. The blood vessels pull away from the dead embryo and form a ring around the yolk. A blood-ring egg won’t develop and should be removed.
Does candling hurt the eggs?
No, as long as you’re quick and gentle. An egg out of the incubator for about 5 seconds cools very little. Use a cool LED light, keep the lid closed between eggs if you can, and avoid shaking or dropping eggs. Most candling damage comes from rough handling, not the light.
Should I remove an egg if I’m not sure it’s alive?
No. Mark it with a question mark, put it back, and recheck in 3 days. A live embryo will be clearly bigger, with stronger veins. A dead one will look the same or show a ring. The only eggs to remove right away are those that smell, ooze or have leaking cracks.
How many times should I candle eggs?
Two or three times for a chicken hatch: day 7, day 14 and optionally day 17 or 18 before lockdown. Candling every day adds handling and cooling without telling you much more. Don’t candle during lockdown unless an egg smells.
Can you candle eggs with a phone flashlight?
Yes, for white and light brown eggs. Hold the blunt end of the egg against the flashlight and cup your hand around it so light can’t leak out the sides. Dark brown, speckled and duck eggs usually need a brighter, dedicated candler.