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Ordinal (Julian) Date Converter

Enter a date or a YYDDD ordinal and pick a direction to convert.

How it is calculated

The tool converts in two directions. Date to ordinal: type a date as YYYY-MM-DD; it must be a real calendar date (30 February is rejected). The day of the year counts from 1 on January 1, and the code is the last two digits of the year followed by the day number padded to three digits: YYDDD. Ordinal to date: type exactly five digits. The year is read with a fixed window: YY 00 to 68 means 2000 to 2068, and 69 to 99 means 1969 to 1999. DDD must be 001 to 365, or 366 only in a leap year. Anything not matching the expected pattern gives no result. This is the manufacturing "Julian" date, not the astronomical Julian Day Number.

Worked example

Convert 15 March 2026 to ordinal form. January has 31 days and February 2026 has 28 (2026 is not a leap year), so March 15 is day 31 + 28 + 15 = 74. The year part is the last two digits, 26, and the day is written with three digits, 074. The code is 26074, and the tool also shows the day of the year as 74 and the year as 2026. Going back the other way, 26074 gives YY 26, which is in the 2000 to 2068 window, so 2026, and day 74 returns 2026-03-15.

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Common mistakes

  • Typing the date as 15/03/2026 or 03-15-2026. The date direction only accepts YYYY-MM-DD, otherwise there is no result.
  • Leaving off the leading zeros when converting back. The ordinal input must be five digits, so day 74 of 2026 is 26074, not 2674.
  • Forgetting the century is lost. 1850-01-05 and 2050-01-05 both become 50005, and the reverse conversion always chooses 2050. Dates before 1969 or after 2068 do not survive a round trip.
  • Assuming a day number past 365 is always valid. Day 366 exists only in leap years such as 2024; 26366 returns nothing.
  • Confusing this with the astronomical Julian Day Number (a count like 2461000) or with the old Julian calendar. This tool only converts between a calendar date and the YYDDD code.

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.

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Comments (1)

  • Editorial team

    In this tool a Julian date means the five-digit YYDDD code seen on food labels and mainframe files, not the astronomical Julian Day number. The century is dropped, so 2026-07-01 becomes 26182 and so would the same day in 1926. When decoding, two-digit years 00 to 68 are read as 2000s and 69 to 99 as 1900s. Which system produced your code?

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