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Julian Date Converter

Convert a calendar date to a Julian date: the day of the year (YYDDD or YYYYDDD, as used on food, military and manufacturing codes) and the astronomical Julian Day Number, and back.

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There are two common meanings of ‘Julian date’. In business, food and military use it means the day of the year (1 to 365 or 366). In astronomy it means the Julian Day Number, a count of days since 1 January 4713 BC. This converter shows both. Two-digit codes are read as years 2000 to 2099.

Quick Answer

A Julian date can mean the day of the year or the astronomical Julian Day Number. For 10 November 2026, the day of the year is 314, so the 5-digit code is 26314 and the 7-digit code is 2026314. Its Julian Day Number at noon is 2,461,355, a running count of days used by astronomers.

Last updated: 10 November 2026 ·How we calculate this: the Fliegel and van Flandern algorithm published by the US Naval Observatory

How This Julian Date Converter Works

Choose what you want to convert. Enter a calendar date to get its day of the year, the 5-digit (YYDDD) and 7-digit (YYYYDDD) Julian date codes, the astronomical Julian Day Number and the Modified Julian Date. Or enter a Julian date code or a Julian Day Number to get the calendar date back, including the day of the week.

Quick explanation: “Julian date” has two meanings.

  • Ordinal date: the day number within the year, 001 to 365 (366 in a leap year). Used on food packaging, military forms and manufacturing lot codes.
  • Julian Day Number: a count of days since noon on 1 January 4713 BC, used in astronomy and computing.

How to Use the Julian Date Converter

  1. Choose the direction of the conversion.
  2. Enter a calendar date, a Julian date code, or a Julian Day Number.
  3. Press Calculate.
  4. Read the day of the year, the codes and the Julian Day Number.
  5. Use the weekday and days left in the year if you need them.

Julian Date Formulas

  • Day of the year: JDN(date) − JDN(1 January of that year) + 1
  • YYDDD code: the last two digits of the year followed by the day of the year with three digits
  • Julian Day Number: the Fliegel and van Flandern integer formula given by the US Naval Observatory
  • Julian Date at midnight: JDN − 0.5 (a Julian day starts at noon)
  • Modified Julian Date: JD − 2,400,000.5

Key Terms

  • Julian date code: a date written as the year and day of the year, such as 26314.
  • Ordinal date: the ISO name for a date written as year and day of the year.
  • Julian Day Number: the number of days since noon on 1 January 4713 BC.
  • Modified Julian Date: the Julian Date minus 2,400,000.5, a shorter day count.
  • Leap year: a year with 366 days, when the day numbers after February shift by one.

Worked Example

A can of food is stamped 26045. What date is it?

  • 26 means the year 2026.
  • 045 means the 45th day of the year.
  • January has 31 days, so day 45 is 45 − 31 = the 14th day of February.
  • The code means 14 February 2026, which is Julian Day Number 2,461,086.

Real-Life Examples

  • Today’s code: 10 November 2026 is day 314, written 26314.
  • Leap year: 31 December 2028 is day 366, code 28366.
  • J2000 epoch: 1 January 2000 at noon is Julian Day Number 2,451,545.
  • Days between dates: subtract Julian Day Numbers: from 1 Jan 2000 to 10 Nov 2026 is 9,810 days.

Julian Date vs Julian Calendar

  • Julian calendar: the old calendar introduced by Julius Caesar, replaced by the Gregorian calendar from 1582.
  • Julian date: a day-of-year code or day count. It is not a date in the Julian calendar.
  • This converter works with Gregorian calendar dates from 1583 onward.

Day of the Year on the First of Each Month

MonthCommon yearLeap year
January11
February3232
March6061
April9192
May121122
June152153
July182183
August213214
September244245
October274275
November305306
December335336

Where Julian Dates Are Used

  • Food and drink: many packers stamp a pack date as YDDD or YYDDD.
  • Military and government: forms and logistics often use YYDDD or YYYYDDD dates.
  • Manufacturing: lot and batch codes record the day of production.
  • Astronomy: the Julian Day Number makes it easy to count days between observations.
  • Software: many systems store dates as day counts, such as the Modified Julian Date.

Common Mistakes to Avoid

  • Mixing up the two meanings. A food code is a day of the year, not a Julian Day Number.
  • Forgetting leap years. After 28 February, leap-year day numbers are one higher.
  • Dropping leading zeros. Day 45 is written 045 in a code.
  • Guessing the century. A 2-digit year is ambiguous; this tool reads it as 20YY.
  • Confusing it with the Julian calendar. They are different things.

Frequently Asked Questions

Enter today’s date: the day of the year and the YYDDD code appear at once.

The first two digits are the year (2026) and the last three are the day of the year (45 = 14 February).

A continuous count of days since noon on 1 January 4713 BC, used in astronomy.

No. Julian dates are day counts or day-of-year codes.

The Julian Date minus 2,400,000.5, so days start at midnight.

In a leap year, 1 March is day 61 instead of day 60.

A short day-of-year code is a compact way to record the pack date.

Usually the last digit of the year plus the day of the year; use the full year to convert it.

Yes, subtract their Julian Day Numbers, or use the Date Calculator.

References & Sources

SourceUsed ForLink
US Naval Observatory, Converting Between Julian Dates and Gregorian Calendar Dates Julian Day Number formulas (Fliegel and van Flandern, 1968). https://aa.usno.navy.mil/faq/JD_formula
US Naval Observatory, Julian Date Converter Official converter for checking results. https://aa.usno.navy.mil/data/JulianDate