Egg cartons from plants producing USDA-graded eggs must display the date the eggs were packed as a Julian date (that is, the day of the year with January 1 being 1 and December 31 day 365). Although not required, egg cartons may also carry an expiration (sell-by) date and/or a best-by (use-by) date.
On egg cartons carrying the USDA grade shield, if an expiration date appears, it can be no more than 30 days after the pack date. Also, on these cartons, if a best-by (use-by) date appears, it can be no more than 45 days after the pack date. However, the packer or quantity purchaser, such as a local supermarket chain, may choose to make the expiration date less than 30 days.
Egg-packing plants not under USDA grading are governed by laws of their states.
Reference: The Incredible Egg website.