Egg Candling Guide: what you should see on day 7, 14 and 18

Candling means shining a bright light through the egg in a dark room to check the embryo. Done on the right days, it tells you exactly which eggs will hatch and which will rot and risk the whole batch. Not sure which days to candle? Use the incubation calculator — it gives you the dates.

🔦 How to candle: dark room, egg on top of the light, big (blunt) end up, work fast (under 30 seconds per egg), and don't candle after lockdown.

Day 7 — first candling: fertile or clear?

✅ Fertile: a dark spot with a spider-web of red veins. Keep it.

❌ Clear / infertile: glows evenly, only a faint yolk shadow. Remove it.

❌ Blood ring: a sharp red circle, no veins — the embryo died. Remove it.

Dark or thick-shelled eggs (Marans, duck) can be hard to read on day 7 — if unsure, mark the egg with a pencil and re-check on day 10 instead of throwing away a live embryo.

Day 14 — second candling: is it growing?

✅ Alive: dark mass fills half the egg; you may see it move. Keep it.

❌ Quitter: murky, sloshing contents, no veins, no movement. Remove it.

Day 18 — final check before lockdown

✅ Ready: all dark except a big, slightly tilted air cell (about ⅓ of the egg). Into lockdown it goes.

The air cell should take roughly a third of the egg by lockdown. Much smaller = humidity was too high; much bigger = too dry. Adjust for your next batch — at day 18 just proceed to lockdown: stop turning, raise humidity, stop opening the incubator.

Candling gear worth having

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High-power LED egg candler

A phone torch works for white eggs; brown and duck eggs need a proper candler.

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Digital thermometer + hygrometer

Air cell wrong size? Your humidity reading is probably lying to you.

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Candling rules that save hatches

Remove clears and blood rings at day 7 — a rotten egg can explode and contaminate every other egg.
When in doubt, keep it and re-check in 3 days. Only discard eggs you are sure about.
Never candle during lockdown (last 3 days) — opening the incubator drops humidity exactly when chicks need it most.
Wash your hands first — shell pores absorb bacteria from your fingers.