I haven't bought eggs for years, as I have my own chickens, but I've used eggs that are 3 weeks old and they've been fine. I don't even keep mine in the fridge. BTW, I think you'll find that the fresher the egg is, the more likely it is to sink in a jug of water and the older it is, the more likely to float, as the air sac in the egg gets bigger, the older it is. If you're not sure, just do what I do and crack it into a cup before you use it. If it doesn't smell, it's OK to eat.