Smell Test: This is the most common and effective method. Crack the egg onto a clean plate and give it a sniff. Fresh eggs should have little to no odor. If there's an unpleasant sulfurous, rotten, or otherwise off smell, the egg is likely spoiled and should be discarded.
Float Test: While not foolproof, the float test can be a quick indicator. Fill a bowl with cold tap water and gently place the egg inside. Fresh eggs will sink to the bottom and lie flat on their side. An egg that floats, especially if it bobs near the surface, might be old and should be double-checked with a sniff test before using. Eggs that sink but stand on one end at the bottom might not be the freshest but can still be okay to use.
Visual Inspection: Crack the egg open and examine the yolk and white. The yolk should be a bright yellow or orange color and appear plump. The white should be clear and translucent, with no discoloration. If you see any bloodspots (usually a small pink speck), it shouldn't necessarily affect the edibility but can be visually unappealing for some. Discard eggs with greenish or brownish discolorations on the yolk or white, or if the white appears cloudy or runny.
Expiration Date: Eggs in the US typically come with a Julian date stamped on the carton. This code represents the day of the year the eggs were laid. However, the expiration date is more of a sell-by date, and properly stored eggs can still be safe to eat for up to 3-5 weeks after the sell-by date. Rely on the smell and visual tests for the most accurate assessment.
Remember: When in doubt, throw it out! It's better to be safe than risk foodborne illness from consuming spoiled eggs.