The egg float test can tell you something about an egg’s age, but it cannot tell you for sure whether the egg is safe to eat.
That’s the part that often gets missed.
A fresh egg usually sinks and lies fairly flat. As the egg gets older, the air cell inside grows larger, so the egg may stand upright or eventually float.
But a floating egg is not automatically rotten, and a sinking egg is not automatically free of harmful bacteria. I use the float test as a quick freshness clue, not as a food-safety test.
If you keep backyard chickens and find an egg you forgot to date, this guide will show you what the float test can tell you, what it can’t, and how I’d check a questionable egg before using it.
What Is the Egg Float Test?
The egg float test is simple. You place an uncracked egg in a bowl or glass of water and watch what it does.
A newer egg usually sinks. An older egg may tilt upward, stand on one end, or float.
People often call this a “bad egg test,” but that name is misleading. What you are really seeing is the effect of the egg’s growing air cell.
If you want more information on egg storage, see How Long Do Fresh Eggs Last?
Why Do Older Eggs Float?
An eggshell looks solid, but it has tiny pores.
After an egg is laid, moisture and carbon dioxide slowly move out through those pores. At the same time, the air cell inside the egg becomes larger.
USDA explains that as this air cell becomes large enough, the egg can become buoyant and float.
So when an egg floats, the simplest interpretation is: this egg is older and has a larger air cell.
It does not mean the float test somehow detected Salmonella, spoilage bacteria, or another invisible food-safety problem.
Egg Float Test: Myth vs. Reality
There are a few egg-float claims I see repeated all the time. Some are partly true, but they’re often taken too far.
Myth: If an Egg Sinks, It Is Safe to Eat
No. A sinking egg is generally fresher, but freshness and food safety are not the same thing.
USDA notes that even clean, unbroken fresh shell eggs can contain Salmonella. Safe handling, refrigeration, and proper cooking still matter.
Myth: Every Floating Egg Is Rotten
Also false.
USDA specifically says that an egg may float because its air cell has enlarged. The egg is older and lower in quality, but it may still be usable.
If I’m unsure about an older egg, I crack it into a small separate bowl first. If it smells bad or looks unusual, I throw it away.
Myth: The Float Test Gives You the Exact Age of an Egg
It doesn’t.
You’ll sometimes see charts claiming that an upright egg is exactly two or three weeks old, while a floating egg is two or three months old. I wouldn’t use those numbers.
Storage temperature, moisture loss, shell characteristics, and starting air-cell size can all affect how quickly an egg changes.
How to Do the Egg Float Test
You don’t need any special equipment.
- A bowl, cup, or glass deep enough to cover the egg
- Cool or room-temperature water
- The uncracked egg you want to check
Then:
- Fill the container with enough water to completely cover the egg.
- Lower the egg gently into the water.
- Watch whether it lies flat, tilts upward, stands more upright, or floats.
- Remove the egg and dry it.
- If you still plan to use an older or questionable egg, crack it into a separate bowl before adding it to your recipe.
I wouldn’t leave eggs sitting in the test water any longer than necessary.
Egg Float Test Chart: What the Positions Really Mean
| What the egg does | What it usually suggests | What it does NOT prove |
|---|---|---|
| Sinks and lies flat | Usually a relatively fresh egg with a smaller air cell | It does not prove the egg is free of harmful bacteria |
| Sinks but tilts upward | Usually older than an egg lying flat | It does not give an exact age |
| Stands upright on the bottom | Older egg with a larger air cell | It does not automatically mean the egg is spoiled |
| Floats | Older, poorer-quality egg with a large air cell | It does not automatically mean the egg is rotten |
Fresh Egg: Sinks and Lies Flat
This is what I’d expect from a fairly fresh egg. The air cell is still relatively small, so the egg stays dense enough to rest flat on the bottom.
Again, “fresh” doesn’t mean “guaranteed safe.” Handle it the same way you would any other raw egg.
Older Egg: Tilts or Stands More Upright
When the large end starts lifting, the air cell has grown.
I’d call this an older egg, not a bad egg. I would not try to assign an exact number of days or weeks from the angle alone.
Floating Egg: Older and Lower Quality
A floating egg has a large enough air cell to make it buoyant.
This tells me the egg is old and the internal quality has probably declined. The white is more likely to be thin and the yolk flatter.
USDA does not say that every floating egg must automatically go in the trash. Their advice is to crack it into a bowl and check for an off odor or unusual appearance before deciding whether to use it.
So, Can You Eat an Egg That Floats?
Possibly, but I’d be more cautious with it.
A float tells you the egg is old. It does not tell you why it’s old, how it was stored, or whether it was kept refrigerated after refrigeration began.
If the storage history is questionable, the shell is cracked, or you have any reason to suspect contamination, I wouldn’t try to rescue the egg just because it smells normal.
If the egg has been handled and refrigerated properly and you’re simply checking an older egg, crack it into a separate clean bowl. A spoiled egg usually makes itself obvious with an unpleasant odor.
What the Egg Float Test Cannot Tell You
This is where I think the float test gets more credit than it deserves.
- It cannot detect Salmonella.
- It cannot guarantee that a sinking egg is safe.
- It cannot tell you an egg’s exact age.
- It cannot replace proper refrigeration.
- It cannot tell you how an egg was handled before you got it.
- It cannot make a cracked or badly contaminated egg safe.
Think of it as a quick quality clue. Nothing more.
A Better Way to Check a Questionable Egg
If I have an older egg and I’m unsure about it, I use a few checks together.
1. Look at the Shell
I wouldn’t use an egg with a badly cracked, leaking, or heavily contaminated shell.
2. Crack It Into a Separate Bowl
Don’t crack a questionable egg directly into your cake batter, skillet, or bowl of six good eggs.
A small separate cup or bowl lets you inspect it without ruining everything else.
3. Smell It
A spoiled egg generally has a strong unpleasant odor when the shell is opened.
If something smells wrong, I don’t debate it. I throw the egg away.
4. Look for Unusual Changes
Older eggs naturally develop thinner whites and flatter yolks. That’s a quality change.
But USDA notes that pink or iridescent egg white can indicate spoilage from bacteria. That is not something I’d eat.
A small blood spot is different. USDA says blood spots come from tiny blood vessels breaking around ovulation and do not, by themselves, mean an egg is unsafe.
More on that here: Blood in Chicken Eggs: Causes and Safety
Does Candling Tell You If an Egg Is Safe?
No.
Candling is useful for seeing the air cell, cracks, internal shadows, and embryo development in hatching eggs. It can tell you a lot about internal quality without breaking the shell.
But it cannot certify that a table egg is free of harmful bacteria.
If you also hatch eggs, see How to Candle Eggs.
What About the Egg Spin Test?
I wouldn’t use spinning as a freshness test.
The classic spin trick is more useful for comparing raw and hard-cooked eggs because the liquid inside a raw egg affects how it spins. It isn’t a dependable way to decide whether a raw egg is fresh or safe.
How Long Do Refrigerated Eggs Last?
For refrigerated shell eggs, USDA’s cold-storage chart lists about 3 to 5 weeks in the refrigerator.
FDA recommends using refrigerated eggs within about 3 weeks for best quality.
I’d store grocery-store eggs in their carton in the main part of the refrigerator at 40°F or below, not in the refrigerator door where the temperature changes more.
Once refrigerated, USDA recommends keeping eggs refrigerated. A cold egg left out can sweat, and that moisture can make it easier for bacteria to move through the shell.
Should You Wash Eggs Before Doing the Float Test?
If you bought USDA-graded eggs at a grocery store, don’t wash them again at home. Commercial eggs have already been washed and sanitized under regulated conditions.
USDA warns that home washing can increase contamination risk because wash water may be drawn through pores in the shell.
Backyard eggs are a little different because practices vary by state and by whether you wash before storage. The safest habit is to collect eggs often, keep nest boxes clean and dry, discard badly damaged eggs, and follow your local Extension or state guidance for washing and selling home-produced eggs.
See our detailed guide on Washing and Cleaning Chicken Eggs.
Does the Carton Date Tell You If an Egg Is Bad?
Not by itself.
Dates such as “Best if Used By” are generally about expected quality, not a magical moment when the food suddenly becomes unsafe.
For eggs, I’d look at the date together with refrigeration history, shell condition, and how the egg looks and smells after cracking.
Egg Float Test as a Simple Science Experiment
The float test does make a nice simple science experiment for kids because you can see buoyancy and egg aging in action.
A reasonable hypothesis would be:
As an egg gets older and its air cell becomes larger, it will become more buoyant in water.
For a better experiment, compare eggs that you know were laid on different dates. Mark the dates on the shells with pencil, keep the eggs refrigerated under the same conditions, and compare how their positions change over time.
Just make sure kids understand that the experiment measures changes associated with age. It is not a test for harmful bacteria.
FAQs About the Egg Float Test
Is the egg float test accurate?
It is useful for showing that an egg has developed a larger air cell and is probably older. It is not accurate as a stand-alone food-safety test.
If an egg sinks, is it definitely good?
No. A sinking egg is generally fresher, but fresh eggs can still carry harmful bacteria. Refrigeration, clean handling, and proper cooking still matter.
If an egg floats, should I throw it away?
Not automatically. USDA says a floating egg is older and poorer in quality but may still be usable. Crack it into a separate bowl and check for an off odor or unusual appearance. If its storage history is questionable, the shell is damaged, or anything seems wrong, discard it.
Why does an old egg stand upright?
As the egg loses moisture and carbon dioxide through the shell, its air cell grows. The larger air cell makes the broad end of the egg more buoyant, so it begins to lift.
Can I tell exactly how old an egg is from the float test?
No. The float position gives you a rough idea of relative age, not an exact laying date.
Are watery egg whites a sign the egg is rotten?
Not necessarily. Egg whites naturally become thinner as eggs age. A foul odor or unusual spoilage-related color is much more concerning.
How long do separated raw egg whites last in the refrigerator?
USDA’s cold-storage guidance lists raw egg yolks and whites at about 2 to 4 days in the refrigerator.
Final Thoughts: Should You Trust the Egg Float Test?
I think the egg float test is useful, as long as you ask it the right question.
If you’re asking, “Is this egg probably newer or older?” the test can help.
If you’re asking, “Can this test guarantee that my egg is safe to eat?” the answer is no.
A floating egg usually has a larger air cell and is older. A sinking egg is generally fresher. Neither result replaces refrigeration, careful handling, proper cooking, or common sense when an egg smells or looks wrong.
That’s the simple rule I’d remember: float test for age, not for safety.
Sources
- USDA Food Safety and Inspection Service: Shell Eggs from Farm to Table
- USDA FSIS: What Does It Mean When an Egg Floats in Water?
- USDA FSIS: Cold Food Storage Guidance
- U.S. Food and Drug Administration: What You Need to Know About Egg Safety
