IncubatorPro
Hatching guide

How to Candle Eggs

Candling means shining a bright light through an egg to see what is happening inside. Done at the right times, it lets you remove bad eggs before they spoil a batch.

By the IncubatorPro team · Updated 26 September 2026

What you need

A bright, narrow torch or a purpose-made egg candler, and a dark room. Work quickly and with clean hands: keep each egg out of the incubator for as short a time as possible.

Day 7: is it fertile?

Fertile and developing: a dark spot (the embryo) with red veins spreading out like a spider. Infertile (“clear”): the egg glows evenly with only a faint yolk shadow. Blood ring: a red ring around the egg with no veins inside means the embryo started and died. Remove clears and blood rings.

Day 14: still developing?

A healthy egg is mostly dark, with the air cell at the blunt end clearly visible and veins near the edge. If you can see the embryo but no movement and the veins have faded, or the contents look cloudy and blotchy, the embryo has probably stopped. Mark doubtful eggs with a pencil and check again in two days rather than removing them straight away.

Day 18: before lockdown

Check the air cell has grown to about a third of the egg and may slope to one side. Remove any egg that smells, weeps or looks cloudy; a rotten egg can burst and contaminate the whole hatch. Then stop turning and go into lockdown. Use the hatch date calculator to get these dates for your batch.

Brown and dark eggs

Brown, speckled and duck eggs are harder to see through. Use a stronger light, candle a day or two later than for white eggs, and compare with a known infertile egg from the same flock.

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FAQ

Common questions

When should I candle chicken eggs?+

On day 7 to check fertility, day 14 to remove eggs that stopped developing, and day 18 before lockdown.

Does candling harm the eggs?+

Not if you work quickly and gently. Keep each egg out of the incubator for as short a time as possible.

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