Egg Freshness Test
The egg freshness test, most often called the float test, uses a simple physics trick to estimate how old an egg is without cracking it open. An eggshell is porous, and as an egg ages, air slowly seeps in through those pores while moisture evaporates out, enlarging the air cell inside. A fresh egg has almost no air cell and sinks and lies flat on its side. An older egg has a bigger air pocket and tilts upright or hovers off the bottom. An egg that floats to the surface has enough trapped air that it has likely gone bad and should be discarded.
Varieties
Shell color (white versus brown) and farming method (caged, cage-free, pasture-raised) have no effect on how the float test works. The test relies on shell porosity and air cell size, which behave the same across all standard chicken egg varieties.
Buying tips
Open the carton at the store and check for cracks before buying. Choose the carton with the latest sell-by date available, and if buying farm-fresh or unwashed eggs with no date, ask the seller how recently they were laid.
Substitutes
Crack and sniff test — N/A
Crack the egg into a clean bowl and check for a sour, sulfurous smell and a runny, spread-out white. A bad egg smells unmistakably off; a fresh one has almost no odor.
Shake test — N/A
Hold the raw egg to your ear and shake it gently. A fresh egg makes little to no sound because the yolk and white fill the shell tightly. A sloshing sound means the contents have shrunk and the egg is older, though not necessarily spoiled.
Candling — N/A
Hold the egg up to a bright light in a dark room. A small, tight air cell and a centered yolk indicate freshness; a large air pocket or visible movement of the yolk signals an older egg.
Sell-by or pack date check — N/A
Not a physical test, but the fastest check: eggs are typically safe for 3 to 5 weeks past the pack date if refrigerated continuously, so the carton date alone often answers the question.
Storage
Store eggs in their original carton on a refrigerator shelf, not the door, where temperature swings speed up aging. Keeping them pointy-end down helps keep the yolk centered and slows air cell growth. Refrigerated eggs stay good for 3 to 5 weeks past the pack date; the float test becomes more useful the closer they get to that window.
How to use
Run the float test before baking, poaching, or eating eggs raw or soft-cooked, since those uses have less margin for error than a fully cooked scramble or hard-boiled egg. It's also useful for eggs that lost their carton or date sticker, or farm-fresh eggs with no printed date at all.
What it pairs with
Fresh eggs with tight whites are best for poaching, frying, and dishes where appearance matters. Slightly older eggs (a week or two past their peak) are actually easier to peel when hard-boiled, since the enlarged air cell makes the shell separate more cleanly from the white.
Nutrition
A large egg has about 70 calories, 6 grams of protein, and 5 grams of fat, along with choline, vitamin D, and B12. Freshness doesn't change the nutrition content meaningfully, only the texture and how the egg behaves when cooked.
FAQ
If an egg floats, is it definitely bad?
Not always spoiled, but it's old enough that the air cell has grown significantly. Crack it into a bowl first and check the smell before deciding to toss it, since some floating eggs are simply on the edge of their usable window rather than truly rotten.
Why does an egg stand upright instead of sinking flat?
An upright egg has a moderately enlarged air cell, meaning it's past peak freshness but usually still fine to eat, especially if cooked thoroughly. This is the most common result for eggs that have been refrigerated for a couple of weeks.
Does the float test work on hard-boiled eggs?
No. Once an egg is cooked, the internal structure changes and the float test no longer reflects freshness accurately. Use the smell and appearance instead for cooked eggs.
Can washing an egg affect the test result?
Store-bought eggs in the US are already washed, so this doesn't change results. But washing removes the natural protective coating called the bloom, which can slightly speed up moisture loss and make an egg age faster than an unwashed one stored the same way.
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