Julian Date Converter
Two different things are both called a Julian date. This Julian date converter gives both, the day-of-year code and the astronomical Julian Day, and says which one you probably mean.
Day of the year
- Day of the year 80 days left in 2026.
- 285 of 365
- YYDDD (5-digit) The short form on lot codes and many manufacturing date stamps. It does not say which century it is in.
- 26285
- YYYYDDD (7-digit)
- 2026285
- ISO 8601 ordinal date
- 2026-285
- Julian Date at 12:00 UTC Days since noon UTC on January 1, 4713 BC, with the time of day as a fraction. The day turns at noon, so midnight is .5.
- 2461326.000000
- Modified Julian Date (MJD) JD minus 2,400,000.5. Smaller numbers, and the day turns at midnight like a civil day. MJD 0 is November 17, 1858, 00:00 UTC.
- 61325.500000
- Julian Day Number of the date The whole-number JD at noon of this calendar date, which is how a date without a time is usually labeled.
- 2461326
- The date
- Monday, October 12, 2026
- If the number is on a food package, a lot code or a military form, it is the day-of-year kind. If it came from astronomy, satellite tracking or a scientific dataset, it is the JD kind.
How the Julian Date Converter works
"Julian date" means two different things, and which one someone means depends almost entirely on where they saw the number.
The first is the ordinal date: the day of the year, counted from January 1 as day 1. October 12, 2026 is day 285, written 26285 in the five-digit YYDDD form or 2026285 as YYYYDDD. ISO 8601 calls this an ordinal date and writes it 2026-285. It is what appears on food packaging and lot codes, on military and government document numbers, on mainframe and manufacturing records, and on anything else where a date needs to be short, sortable and free of month names. Nothing about it is Julian; the name is a long-standing misnomer, borrowed from the astronomical count because both are "days numbered in a row".
Reading one is straightforward with two traps. A five-digit code does not carry its century, so 26285 could be 2026 or 1926. That is obvious for a can of beans, less so for a records archive. And in a leap year every day number from 060 onward lands one calendar day earlier than in a common year: day 060 is February 29 in 2028 and March 1 in 2026. A code converted with the wrong year's leap status is off by a day for ten months.
The second is the astronomical Julian Date: a continuous count of days since noon UTC on January 1, 4713 BC in the proleptic Julian calendar, with the time of day as a decimal fraction. Noon on January 1, 2000 is JD 2,451,545.0; the Unix epoch, midnight on January 1, 1970, is JD 2,440,587.5. Astronomers use it because it removes calendars from arithmetic entirely: the interval between two observations is one subtraction, across any number of months, leap years or calendar reforms. The day begins at noon because that suited astronomers observing through the night, which is why a JD at midnight ends in .5.
The Modified Julian Date subtracts 2,400,000.5. That shortens the number by two digits and moves the day boundary to midnight, so MJD 61,325 is a whole civil day (October 12, 2026) rather than two halves of one. Satellite tracking, geodesy and many scientific datasets use MJD.
Two precision points. J2000.0, the reference epoch JD 2,451,545.0, is strictly defined in Terrestrial Time (TT), which ran about 64 seconds ahead of UTC in 2000; this converter treats every input as UTC, which is right for anything short of precision astronomy. And dates before October 15, 1582 are read on the proleptic Gregorian calendar. Astronomical software, including the US Naval Observatory's converter, switches to the Julian calendar for earlier dates, so the same JD is labeled with a date about ten days different there.
If you are holding a package, a form or a lot code, you want the day-of-year answer. If the number has seven digits before a decimal point and starts with 24, it is an astronomical JD.
Julian Date Converter FAQ
What is today's Julian date?
The date field fills in with today's date from your device when the calculator loads, and the answer follows it. The example the page is served with is October 12, 2026: day 285 (26285 or 2026285), and the astronomical Julian Date at noon UTC is 2,461,326.0.
How do I read a Julian date code on food packaging?
The last three digits are the day of the year and the digits before them are the year. 26285 is day 285 of 2026, which is October 12. Some packers use a single year digit, so 6285 would also be day 285 of a year ending in 6.
What is the difference between JD and MJD?
MJD is JD minus 2,400,000.5. The subtraction shortens the number and moves the start of the day from noon to midnight, so an MJD lines up with civil days. JD 2,461,326.0 is MJD 61,325.5.
Why does the Julian Date start at noon?
It was designed for astronomers, who observe at night. Starting the day at noon keeps a whole night's observations on one day number.
Is the Julian date related to the Julian calendar?
The astronomical count is anchored in the Julian calendar (day 0 is January 1, 4713 BC on it), but it is a plain day count, not a calendar. The day-of-year code has nothing to do with the Julian calendar at all; the name is a misnomer.