MRE Manufacturers use a 4-digit modified julian date code to indicate the manufacture date. This code is usually stamped on the MRE box and pouch. The location of the code can vary. The first digit represents the year, and the last three digits represent the day. Date code 7304 = 304th day of 2007. Sometimes other letters representing batch numbers will be appended to the date code (i.e. 7304C). Since the official longevity of an MRE is no longer than 10 years, and the modified date code makes it impossible to determine the decade of manufacture, this calculator assumes that your MREs are not 10 years old or more.