About the Julian Date Converter
This Julian date converter handles the two very different things people call a “Julian date”. In manufacturing, food packaging, the military and mainframe systems, a Julian date is an ordinal date: the year followed by the day of the year, such as 26045 (YYDDD) or 2026045 (YYYYDDD) for 14 February 2026. In astronomy, the Julian Date (JD) is a continuous count of days since noon on 1 January 4713 BC, such as 2461313.0.
Choose what you have — a calendar date, an ordinal Julian date, or an astronomical JD — and the converter returns every other form: the calendar date and weekday, the YYDDD and YYYYDDD codes, the Julian Day and the Modified Julian Day (MJD). Use it to decode a lot or expiry code on a product, read a date stamp on military paperwork, or prepare timestamps for astronomy software.
For five-digit YYDDD codes the century is ambiguous, so pick it from the list. Astronomical Julian Dates start at noon UTC, so the time of day matters; calendar dates are treated as the proleptic Gregorian calendar.
How to use the julian date converter
- 1Choose what you are starting with: a calendar date, an ordinal Julian code, or an astronomical JD.
- 2Enter the date and UTC time, the 5- or 7-digit code, or the JD value.
- 3For 5-digit codes, select the right century.
- 4Read the converted date, the YYDDD and YYYYDDD codes, and the JD and MJD.
Formula and method
The ordinal (“Julian”) date used on packaging and in the military is simply the year followed by the three-digit day of the year: 1 January is 001, 31 December is 365 or 366. To decode it, add (DDD − 1) days to 1 January of that year.
The astronomical Julian Day is a running count of days that starts at noon UTC on 1 January 4713 BC (Julian calendar). Midnight at the start of 1 January 1970 is JD 2,440,587.5, so the converter adds that constant to the day count since 1970 and the fraction of the day. The Modified Julian Day subtracts 2,400,000.5, so it starts at midnight and has fewer digits.
- JD
- Julian Day — days since noon UTC, 1 January 4713 BC
- MJD
- Modified Julian Day — JD − 2,400,000.5, starting at midnight
- YYDDD
- Two-digit year and three-digit day of the year
Worked examples
Calendar date to Julian date: 29 Sep 2026 at noon UTC
29 September is the 272nd day of 2026, so the ordinal Julian date is 26272. At 12:00 UTC the astronomical Julian Day is exactly 2,461,313.0 and the MJD is 61,312.5.
Decode the code 26045
The code 26045 means year 2026, day 045. Adding 44 days to 1 January gives Saturday 14 February 2026.
Seven-digit code in a leap year
2024 was a leap year with 366 days, so day 366 is 31 December 2024.
Astronomical JD to date and time
JD 2,451,545.0 is the J2000 epoch, noon UTC on 1 January 2000. Adding a quarter day (0.25) moves it to 18:00 UTC the same day.
Frequently asked questions
What is a Julian date on food packaging?+
It is usually the day of the year, often with the last digit or two of the year in front. For example 26045 means the 45th day of 2026 — 14 February. Some makers shorten it to four digits (6045); enter that here as 26045. Manufacturers use it to track lots and production dates.
What is today’s Julian date?+
Enter today’s date. As a reference, 29 September 2026 is 26272 (YYDDD), 2026272 (YYYYDDD), and Julian Day 2,461,313.0 at noon UTC.
Is a Julian date the same as the Julian calendar?+
No. The Julian calendar is the calendar introduced by Julius Caesar and replaced by the Gregorian calendar from 1582. Julian Day numbers and ordinal “Julian dates” are day-counting systems, not calendars; the JD count merely has its starting point defined in the Julian calendar.
Why does the astronomical Julian Day start at noon?+
Astronomers chose noon so a whole night of observations falls on a single Julian Day number. As a result, midnight UTC always ends in .5, for example JD 2,461,312.5 for the start of 29 September 2026.
What is the Modified Julian Date (MJD)?+
MJD = JD − 2,400,000.5. It begins at midnight instead of noon and uses smaller numbers, which is why it is common in astronomy, satellite tracking and space-science datasets.