Julian Date Calculator App | The sell-by date for eggs can be up to 45 days after packing. Every egg carton has a code on its side; the last 3 numbers are the Julian date. Numbers from 001 to 365 correspond to a day of the year: the packaging date. 001 is Jan 1st and 365 is Dec 31st. For freshness, select the highest number you can find (the numbers wrap around in Jan). Or just use the app to convert the number to the packing date.