Egg Freshness Calculator

How to tell if eggs are still good

The float test is the most popular method and the most misunderstood one. An egg that floats is not automatically rotten. An egg that sinks is not automatically fresh. The test measures the size of the air cell, which grows as moisture evaporates through the shell over time. Here is what each result actually means.

Quick context on where these figures come from. We built Flockmath because most online answers to "are my eggs still good?" jump straight to "if it floats, throw it out" without explaining what the float test actually measures. The calculator above estimates age from your lay date and storage method, then predicts the float result so you know what to expect before the egg ever hits the water. The float test is still the final word — this just tells you what is normal for an egg of that age.

How long do eggs last? Shelf life by storage method

Storage method matters more than anything else for how long an egg keeps. Here is the full range the calculator uses, with a store-bought reference row for comparison:

The store-bought row counts from the pack date, not the lay date. Commercial eggs may already be a week or more old by the time they are washed, graded, and packed, so the USDA’s 3-to-5-week refrigerated window and our longer from-lay figures start from different points — they are not in conflict.

These are quality-and-safety windows for properly stored eggs. The float test and a smell check after cracking remain the final word on an individual egg’s freshness, whatever its age on paper.

The float test explained

Place the egg in a bowl or glass of cold water deep enough for the egg to be fully submerged, then read the result against its approximate age:

One caution the test cannot capture on its own: it measures buoyancy, not safety. A well-preserved old egg with an intact bloom can still sink, and a washed egg can float before it actually spoils. Use the float result as an age estimate, then confirm with your nose after cracking.

Room temperature vs refrigerated — a genuine difference

Outside the US, most people store eggs at room temperature and consider them fresh for 2 to 4 weeks. This works because unwashed eggs retain their natural cuticle (called the bloom), which seals the porous shell and slows moisture and bacteria penetration.

In the US, commercial eggs are washed — removing the bloom — making refrigeration necessary to prevent bacterial growth. If you have backyard chickens and do not wash the eggs, room-temperature storage keeps them well for 2 to 4 weeks and is how most of the world stores eggs.

If you do wash your eggs before storing, refrigerate them. Washing removes the bloom and the egg is then vulnerable to bacteria at room temperature.

Water glassing — the long-term storage method

Water glassing uses a solution of calcium hydroxide (pickling lime) and water to seal unwashed fresh eggs for long-term storage. Properly water-glassed eggs in a sealed container stay edible for 12 to 18 months at cool room temperature.

The process requires fresh, unwashed, uncracked eggs and clean water. The lime solution coats the shell and prevents moisture loss and bacterial entry. It was the standard egg preservation method before refrigeration.

Water-glassed eggs work fine for baking and cooking. They are not ideal for frying sunny-side up because the texture changes slightly. But for an omelette, cake, or scrambled eggs the difference is undetectable.

One honest caveat: water glassing is a traditional, pre-refrigeration method, not a modern food-safety-tested one. We could not find a USDA validation or an extension-service endorsement of it, so treat the 12-to-18-month figure as traditional practice and our own estimate rather than tested guidance. It depends entirely on the eggs being fresh, unwashed, uncracked, and cuticle-intact — and because it is unvalidated, water-glassed eggs are best cooked thoroughly, until the yolk and white are firm, rather than eaten raw or lightly cooked.

Best uses for eggs at different stages

Very fresh (under 1 week): poaching, frying, soft-boiling — anywhere presentation matters and the texture of a fresh yolk is noticeable.

Fresh (1 to 3 weeks): all uses. No meaningful quality difference for most cooking applications.

Use soon (3 to 5 weeks): scrambling, baking, hard-boiling. Notably easier to peel when hard-boiled — this is one practical advantage of slightly older eggs.

Past peak (5+ weeks at room temp, smell test first): baking where the egg is one of many ingredients. The smell test reliably catches spoilage — a rotten egg has an unmistakable sulfur odor, so an egg that smells normal has not spoiled. That is not the same as a guarantee of safety (see the note on freshness versus safety below), but it has not gone off.

Freshness and safety are two different questions

This calculator answers the freshness question — how old an egg is and what it is best used for. Safety is a separate question, and neither the float test nor the smell test answers it. Both catch spoilage: an egg broken down by bacteria looks and smells wrong, and the smell test reliably flags it. Neither catches Salmonella. According to the CDC, food contaminated with Salmonella usually looks, tastes, and smells completely normal, and a hen can carry it and pass it into a clean, intact, normal-looking egg without appearing sick herself — so for a backyard flock this matters a little more, not less. The per-egg risk is small, on the order of 1 in 10,000 where the bacterium is present, but you cannot smell or float-test around it. Three habits cover it, per the CDC and USDA FSIS: keep eggs refrigerated, cook them until the yolk and white are firm (160°F / 71°C in dishes), and wash your hands and surfaces after handling eggs or hens. None of this makes your eggs dangerous — it means a normal-smelling egg is reassuring about spoilage, not a guarantee of safety.

Common mistakes

1. Assuming a floating egg is rotten and discarding it without smelling it. A floating egg has a large air cell, which means age — not necessarily spoilage. Smell it first.
2. Refrigerating washed eggs on the counter, then putting them back in the fridge. Temperature cycling accelerates moisture loss.
3. Storing eggs near strong-smelling foods in the fridge. Eggshells are porous and eggs absorb odors.
4. Not dating the eggs when you collect them. A simple pencil mark with the collection date on the egg takes 2 seconds and saves all the guessing this calculator is designed to help with.
5. Discarding an egg that cracks while you handle it. If it cracks at home, break it into a clean container, cover it, refrigerate, and use within 2 days (USDA FSIS). Eggs already cracked when you buy or collect them are the exception — discard those.

Where to go next

Knowing how fresh your eggs are is one piece of the backyard egg picture. A few connected calculators:

• The Egg Production Calculator estimates how many eggs your flock will lay each week and year, so you know how fast the carton fills up in the first place.
• The Eggs Per Family Calculator works the other direction: how many hens you need to match your household's egg habit without a constant surplus.
• The Feed Consumption Calculator tells you what those eggs cost to produce, broken down by breed and life stage.
• The First-Year Cost Calculator adds up the full startup cost of a flock — coop, birds, equipment, and feed — plus your year-two operating cost.

Sources

• Shelf life, safe handling, and cooking: USDA FSIS — “Shell Eggs from Farm to Table.”
• Salmonella: CDC — “Preventing Salmonella Infection.” Food contaminated with Salmonella usually looks, tastes, and smells normal, so the smell test cannot detect it.
• Refrigerated shelf life: USDA Agricultural Research Service — “How We Store Our Eggs—and Why.” In a 5,400-egg study, refrigerated eggs (washed or oiled) averaged Grade A quality at 15 weeks, which is why our 10-week unwashed-fridge figure is deliberately conservative.
• Safe handling for small flocks: University of Minnesota Extension — “Safety tips for handling farm fresh eggs” (shelf life from pack date, discard cracked eggs, cook until firm or to 160°F).

Some values here are our own. The float-test age bands (all six) are ours, derived from how the egg’s air cell grows with age rather than a published table. The 12-to-18-month water-glassing figure is a traditional-practice estimate with no USDA or extension validation we could find. The cool-pantry/cellar figure (about 5 weeks) is also ours.