Egg Candling 101: You Just Got Fertile Eggs in the Mail… Now What?

Fertile Eggs Just Arrived? Here’s How to Check If They’re Developing

Your fertile eggs just arrived from USPS, and if you’re like most first-time incubator owners, the first thing you’re wondering is:

Are these actually fertile?

You open the box carefully, check for cracks, and gently lift each egg out. From the outside though, there’s no way to tell what’s happening inside. A fertile egg looks exactly like a non-fertile egg before incubation begins.

At this stage…

They all look the same.

What Would Candling Look Like Today?

If you candle the egg right now — the day it arrives — you’ll likely see a warm yellow glow, the shadow of the yolk, and a small air cell at the blunt end.

But that’s it.

No veins.
No embryo.
No movement.

Even fertile eggs will look completely clear on Day 0 because development hasn’t started yet.

Option A: The… Educational Route

If you're really curious, you could perform an egg-topsy by cracking open an unincubated egg and looking for the blastoderm — the tiny white bullseye on the yolk that indicates fertility.

You’re looking for:

• A small white dot (non-fertile)
• Or a white ring / bullseye (fertile)

But now you’re down one egg.

So you can either learn about egg development cycles the messy way…
or just keep reading this article.

Step 1: Let Your Eggs Rest First

Shipped eggs go through temperature swings, vibration, and pressure changes that can shift the air cell inside the shell during transit. Before setting them in the incubator, give them time to settle so internal structures can return to their proper position.

Allow your eggs to rest:

• 12–24 hours
• Pointy end down
• At room temperature

Skipping this step can reduce hatch rates before incubation even begins.

Step 2: Start Incubation

Now it’s time to place your eggs into the incubator using the standard starting settings for chicken eggs:

• Temperature: 99.5°F
• Humidity: 40–50%

Before placing your eggs inside, take a pencil and mark:

• One side with an X
• The opposite side with an O

This helps you confirm that your eggs are fully turning each day — especially if you're rotating them by hand. It’s surprisingly easy to roll an egg partway and assume it’s been turned when it hasn’t.

Keeping track matters.

Many hatchers also keep an incubator log book to record:

• Temperature checks
• Humidity levels
• Turning schedule
• Candling results
• Hatch day progress

Once everything is set, turn on automatic egg turning if available or rotate eggs by hand several times per day.

Then you wait.

Step 3: When Will You See Something?

During the first few days of incubation, you still won’t see much. Even fertile eggs can appear completely clear through Day 1, Day 2, and Day 3 because embryo development is happening on a microscopic level.

But by Day 5–7…

Things start to change.

You may begin to see:

• Thin red veins
• A spider-like web pattern
• A small dark embryo

This is the circulatory system forming — and it’s the first visible sign of life inside the egg.

Which Eggs Are Harder to Candle?

Some eggs are naturally difficult to see through due to shell pigment or thickness, which can make early candling results confusing.

You may struggle to candle:

• Dark brown eggs (Marans, Welsummers)
• Olive eggs (Olive Eggers)
• Blue eggs (Ameraucanas, Cream Legbars)
• Speckled quail eggs
• Thick duck or goose eggs

Dark pigment blocks light, speckles scatter the beam, and thicker shells reduce how much light reaches the embryo inside.

Sometimes fertile eggs from these breeds can look totally clear — or just shadowy — even when they’re developing normally.

If you’re unsure:

• Wait and candle again in 3–4 days
• Look for air cell growth
• Watch for the egg becoming darker over time

Development may still be happening.

Track Egg Weight Loss Over Time

If you can’t see through the shell clearly, you can track what’s happening inside by weighing the egg instead. As the embryo develops, moisture slowly leaves through tiny pores in the shell so the air cell can grow and the chick has room to move into hatch position.

For chicken eggs, you should expect:

• About 11–13% total weight loss by hatch day
• Roughly 0.5–0.7% per day

Even if veins aren’t visible, you may still notice:

• The egg becoming slightly lighter
• The air cell gradually enlarging

If the egg is losing:

• Too much weight → Humidity may be too low
• Too little weight → Humidity may be too high

Sometimes the scale tells you more than the flashlight can.

Day 10–14: Rapid Growth

By the second week, the embryo is growing quickly and taking up more internal space. Candling during this stage usually shows:

• A darker internal mass
• Fewer visible veins
• Movement when tilted gently
• A defined air cell

This is when many first-time hatchers finally feel relief.

Something is actually in there.

Day 18: One Last Candling Check

Before lockdown, do one final candling session to remove any eggs that stopped developing earlier in incubation.

You’re looking for eggs that appear:

• Completely clear
• Cloudy
• Or have a blood ring

These are often called quitters.

Leaving them inside the incubator during lockdown can lead to bacterial buildup and internal pressure — and eventually a rotten egg can burst open inside the incubator.

Also known as:

A stink bomb.

Remove any non-developing eggs now before humidity increases for lockdown.

When NOT to Candle

Once lockdown begins (after Day 18 for chickens), candling should stop completely. At this point, the chick is positioning to hatch and the inner membrane becomes delicate.

Opening the incubator now can cause:

• Shrink wrapping
• Failed internal pips
• Stuck chicks

Resist the urge.

Hands off until hatch day.

Candling gives you a small window into what’s happening inside the shell and helps you make smart decisions during incubation.

If you see veins by Day 5–7…

You’re on the right track.

Now it’s just a matter of time.