Ordinal (Julian) Date Converter

About this calculator

An ordinal date — often called a “Julian date” in manufacturing and logistics, though it’s unrelated to the astronomical Julian Day Number — identifies a calendar day by its year and its sequential position within that year rather than by month and day. In the common 5-digit YYDDD form, YY is the two-digit year and DDD is the day-of-year count from 001 to 365 (or 366 in a leap year), so December 31, 2026 would be written 26365.

This format is standard in food and pharmaceutical manufacturing (stamped on packaging as a lot or “best by” code), military logistics, and some aviation and government recordkeeping, because a single unambiguous number is faster to stamp, scan, and sort than a month/day pair, and it makes shelf-life and expiration calculations a matter of simple subtraction. This calculator converts a standard calendar date into its YYDDD ordinal form and back again in either direction.