How to Candle Chicken Eggs Day by Day
The short version
Day-by-day schedule
| Day | Phase | What to do |
|---|---|---|
| Days 1–3 | Too early to read | Nothing useful shows yet on most eggs. Blood vessels and the heartbeat begin forming around day 2 per eXtension, but they are far too small to see through the shell. Resist candling now — you will only cool the eggs and risk handling damage. Wait for day 4 at the earliest. |
| Days 4–7 | First candling — veining | This is the first reliable check. Mississippi State Extension notes eggs are normally tested after 4 to 7 days. A developing embryo looks 'spider-like' — a small dark body with large blood vessels spreading out like a spider's legs. You may catch a faint pulsing beat. White and light-shelled eggs read earlier and more clearly than dark or tinted ones. |
| Days 8–10 | Movement | The vein network is dense and the embryo is a distinct dark mass that often jerks or drifts when the light warms it. Toes and feather buds are developing internally. Clears (no veins, just the yolk shadow) and quitters (a blood ring or a stalled dark spot with no fresh veining) are easy to spot now and should be removed. |
| Days 11–14 | Filling | The embryo fills much of the egg and the veined area darkens; less clear space remains at the pointed end. By about day 14 the embryo turns to point its head toward the air cell. Down is forming on the body. A living embryo still shows movement against the light at the edges of the dark mass. |
| Days 15–17 | Mostly dark | The egg candles mostly opaque — a dark chick filling nearly the whole shell with a distinct, sharply bordered air cell at the large end. This is your last easy read before lockdown. Confirm the air cell is growing; a small air cell means humidity has run too high, a huge one means too low. |
| Day 18 | Air cell drawn down — stop | At lockdown the air cell should occupy roughly the top third of the egg and its border often looks tilted or 'drawn down' on one side as the chick prepares to internally pip. Do a final candle if you must, then stop opening the incubator until hatch — repeated candling now risks chilling and shrink-wrapping. |
Equipment and setting up a dark room
You need two things: darkness and a bright, focused light. Candle in a fully dark room at night, or in a closet, so the only light is the beam passing through the egg. A purpose-built egg candler works best, but a small high-output LED flashlight is fine — the key is that the beam is narrow and bright so it lights the interior instead of leaking around the shell.
Cup the egg large-end (air-cell end) against the light and seal the gap with your hand so no light escapes around the edges. Rotate the egg slowly to bring the veins and embryo into view. Work quickly — a minute or two per egg is plenty — and return eggs to the incubator promptly so they don't cool. Warm hands and a warm room help; avoid setting eggs down on cold surfaces.
What a healthy embryo looks like — and what a clear, quitter, or blood ring looks like
A fertile, living embryo is, in Mississippi State Extension's words, 'spider-like in appearance, with the embryo representing a spider's body and the large blood vessels spreading out much like a spider's legs.' From day 4–7 onward you should see that web of veins, and by day 8–10 the embryo often moves when the warm light hits it. As development continues the dark mass grows until, by the mid-teens, the egg candles mostly opaque with a clean air cell at the top.
A clear egg looks exactly as it did when you set it — Mississippi State describes an infertile egg as appearing 'as a clear egg except for a slight shadow cast by the yolk,' with no veins. A quitter is an embryo that started and then died: it shows a stalled dark spot with no fresh, spreading veins, and often a blood ring — a ring or streak of blood around the embryo caused by 'the movement of blood away from the embryo after death.' Extension guidance is to remove all clears and any egg showing a blood ring or streak so they don't rot and burst among the good eggs. When you can't tell a slow embryo from a quitter, leave it and re-candle in 2–3 days: a live embryo will have visibly grown.
Candling dark, tinted, and shipped eggs
Brown, olive, and heavily tinted shells block far more light than white or cream eggs, so veining is harder to read. Use your brightest light, candle in the darkest room you have, and give dark eggs an extra day or two before the first check so there is more embryo to see. Marans and other very dark eggs may never candle crisply — judge by the growing dark mass and the air cell rather than expecting fine vein detail.
For shipped eggs, the air cell is the extra thing to watch: transit can detach or 'saddle' the air cell, and candling lets you confirm whether it has re-settled to the large end. Track the air cell's growth across candlings as your humidity gauge. This guide is about reading development, not diagnosing sick birds or embryos — for health questions, see a veterinary reference such as PoultryDVM, and consult a vet for anything requiring treatment.
Common pitfalls
- Candling too early (days 1–3) and concluding an egg is a clear when it simply hasn't developed enough to read yet.
- Using a dim or wide flashlight instead of a bright, focused beam sealed against the shell — ambient light washes out veining.
- Mistaking the normal yolk shadow in a fresh clear egg for an embryo, or vice versa; when unsure, re-candle 2–3 days later and look for change.
- Handling eggs with cold hands in a cool room for minutes at a time — candle quickly and return eggs to the incubator.
- Candling dark or heavily tinted eggs with too little light and pulling viable embryos you simply couldn't see.
Frequently asked questions
- When should I candle chicken eggs?
- Do your first candling around day 4–7, when a fertile egg shows a spider-like network of veins. Candle again around day 10 to confirm movement and pull clears and quitters, and once more before lockdown on day 18 to check the air cell. Avoid candling on days 1–3 (nothing reads yet) and after day 18 (it risks chilling the chicks).
- What does a fertile egg look like when candled?
- From day 4–7 a fertile egg shows a 'spider-like' dark embryo with blood vessels spreading out like a spider's legs, and often a faint heartbeat. By day 8–10 the embryo is a distinct dark mass that moves when the light warms it, and by the mid-teens the egg candles mostly dark with a clear air cell at the large end.
- What is the difference between a clear, a quitter, and a blood ring?
- A clear is infertile (or died before any growth showed) — it looks like a fresh egg with only the yolk shadow and no veins. A quitter started developing and then died: a stalled dark spot with no fresh veining. A blood ring is a ring or streak of blood, a sign the embryo died and its blood pulled away. Remove clears, quitters, and blood-ring eggs so they don't spoil.
- How do I candle dark or tinted eggs?
- Use your brightest, most focused light in the darkest room you have, seal your hand around the shell so no light leaks, and give dark eggs an extra day or two before the first candling so there's more to see. Very dark shells (like Marans) may never show crisp veins — judge by the growing dark mass and the air cell instead.
- Can candling hurt the eggs?
- Not if you're quick. Candle in short sessions, keep your hands and the room warm, and return eggs to the incubator promptly so they don't chill. Avoid frequent candling after day 18 (lockdown), when opening the incubator drops humidity and can shrink-wrap pipping chicks.
- My egg looks clear on day 7 — should I throw it out?
- If it's a light-shelled egg with no veins at all by day 7, it's very likely infertile. When you're unsure — especially with dark or tinted eggs — leave it and re-candle in 2–3 days. A live embryo will have visibly grown and veined; a truly clear egg won't change.
Sources
- Testing incubated eggs for embryo development (candling) — Mississippi State University Extension Service (University extension)
- Avian Embryology (day-by-day embryo development) — eXtension — Poultry (University extension)
- Candling Eggs — University of Illinois Extension (University extension)