There’s a row of numbers stamped on the end of every carton of eggs in the shop. Most of us have never looked at it, and the ones who have assume it’s a batch code for the factory.
One of those numbers tells you the exact day the eggs were packed. Not “best by” — packed. And it is very often a different answer from the date printed on the front.
The Three-Digit Number Is a Date
Look for a three-digit number between 001 and 365. That’s the Julian date — the day of the year the eggs went into that carton.
001 is January 1st. 365 is December 31st. Everything else counts up in between.
So a carton stamped 262 was packed on the 262nd day of the year, which is the 19th of September.
You don’t need to do that arithmetic in the shop. You only need to compare — of two cartons on the shelf, the higher number was packed more recently. That’s the whole skill.
The only exception is around New Year, when a low number like 004 is newer than 360, not older.
The Other Number: the Plant Code
Next to it you’ll usually see something starting with P, like P-1234.
That’s the plant code — it identifies the facility that packed them. It’s not much use day to day, but it’s the number that matters during a recall, because recalls are announced by plant code and Julian date rather than by brand.
Worth knowing it’s there. Not worth thinking about otherwise.
Why It Beats the Date on the Front
The date printed on the front of the carton — “sell by”, “best by”, “use by” — is set by the producer, and different producers give themselves different windows from the same packing day.
So two cartons can carry the same “best by” date and have been packed a week apart.
The Julian date can’t be adjusted like that. It’s the actual day. When two cartons look identical on the front, it’s the only thing that separates them.
How Long Eggs Actually Last
Longer than most people think. Refrigerated eggs are generally good for three to five weeks past the packing date, and that’s well beyond the date printed on the carton.
They don’t go off sharply. They slowly lose moisture through the shell and the white gets thinner and runnier — which is why an older egg spreads out in the pan instead of sitting up.
That makes older eggs better for hard boiling, by the way. A very fresh egg is notoriously hard to peel. Two or three weeks old and the shell comes away cleanly.
The Float Test, and What It Really Tells You
Put an egg in a glass of water.
Sinks and lies flat — fresh. Sinks and stands on end — older but fine. Floats — throw it out.
What’s happening is the air pocket inside grows as moisture escapes through the shell. A big enough pocket makes it buoyant.
One honest caveat: this tests age, not safety. A floating egg is old and should go. But an egg that sinks isn’t automatically safe — if it smells wrong when you crack it, that’s the answer, whatever the glass said.
Always crack into a separate bowl first. One bad egg shouldn’t take a whole batch of batter with it.
Storing Them Properly
Leave them in the carton. It protects the shells and it stops them absorbing smells, because eggshells are porous and will happily take on whatever is near them.
And keep them off the fridge door, even though the door is where the egg rack usually is. The door is the warmest part of the fridge and eggs keep better at a steady temperature.
Middle shelf, in the carton they came in.
Ten Seconds at the Shelf
Next time, turn the carton and look at the short end. Find the three-digit number, and take the highest one on the shelf.
It costs nothing and it is the only honest measure of how fresh those eggs actually are.
