The short answer: yes, sometimes. The float test can tell you whether an egg is old, because eggs naturally lose moisture over time and the air cell inside gets larger. But it does not tell you for sure whether an egg is safe to eat.
Here is what is happening inside the shell. A fresh egg has very little air inside, so it usually sinks and lies flat in a bowl of water. As days and weeks pass, water slowly evaporates through the porous shell and air replaces it. That bigger air pocket makes the egg more buoyant, so an older egg may stand upright on the bottom or float higher in the water.
How to read the float test
- Sinks and lies flat: very fresh.
- Sinks but stands upright: older, but often still usable soon.
- Floats: quite old; quality is likely poor and the egg should be checked carefully before using.
The important part is that buoyancy is a clue about age, not a laboratory safety check. An egg can be relatively old and still fine if it has been stored properly and the shell is intact. On the other hand, an egg can spoil before it becomes dramatically buoyant if it has been contaminated, kept too warm, or damaged.
If you want a more practical kitchen rule, use the float test as a first filter, then break the egg into a separate bowl and judge it with your senses. A fresh egg should have a compact yolk, a thicker white, and a neutral smell. If it smells sulfurous, rotten, or just obviously off, discard it immediately, no matter what the water test suggested.
What the test does not guarantee
The float test cannot detect every safety issue. It will not tell you whether bacteria are present, whether the egg was contaminated after cracking, or whether the shell has microscopic damage. It also does not replace proper refrigeration and sensible storage. For that reason, a floating egg is best treated as a warning sign of age, not as a yes-or-no verdict on edibility.
My practical advice: keep eggs cold, use them within a reasonable time, and trust the float test only as a rough kitchen shortcut. It is helpful, quick, and easy to remember, but it works best when combined with the smell test, a visual check, and common sense.
Try it with this recipe: https://en.alwaysyummy.recipes/the-perfect-egg-and-cheese-sandwich-in-10-minutes/