Julian Date Calculator
Convert a calendar date to its Julian date, as a day-of-year code (YYDDD or YYYYDDD) or an astronomical Julian Day, and convert either one back to a date.
A Julian date usually means the day of the year written after the year: 6 October 2026 is day 279, so its Julian date is 26279 in the five-digit YYDDD form used on food packaging, military paperwork and batch codes, or 2026279 with the full year. Astronomers mean something else, the Julian Day, a running count of days that reaches 2461320 at noon UTC that day. This calculator converts both ways for both kinds.
This calculator uses the Gregorian calendar extended back before 1582 and covers years 1 to 9999 only; it does not convert to or from the old Julian calendar, ignores leap seconds, and works in UTC, so a local date near midnight can fall on a different day. Some companies use their own lot-code formats, so check a manufacturer's code key if a result looks wrong.
Date to Julian date
Tuesday, October 6, 2026
Day 279 of 365
- YYDDD code
- 26279
- YYYYDDD code
- 2026279
- Days left in the year
- 86
- Julian Date (astronomical, 12:00 UTC)
- 2461320.00000
- Modified Julian Date
- 61319.50000
Julian date to calendar date
Calendar date
Tuesday, October 6, 2026
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About the Julian Date Calculator
The two meanings of Julian date share a name and little else. The ordinal kind numbers the days of each year from 001 to 365, or 366 in a leap year, and writes them after the year: 31 December 2024 was day 366 of a leap year, so its code is 24366. These codes show up as pack dates on cans and eggs, in military and government date fields, and in manufacturing lot numbers; a five-digit code does not say which century it belongs to, so the calculator reads it in the 2000s unless you pick another. The astronomical kind is a single count of days with no years or months at all, used to measure the time between observations. Day 0 began at noon UTC on 1 January 4713 BC in the Julian calendar, and the day starting at noon on 1 January 2000 was Julian Day 2451545. Because each Julian Day starts at noon, the calculator asks for a UTC time and shows the fraction of the day, and it also shows the Modified Julian Date, which subtracts 2,400,000.5 so that its days start at midnight. Dates are in the Gregorian calendar we use today, extended backward before 1582, for years 1 to 9999.
Frequently asked questions
What is today's Julian date?+
Press the button to use the current date and time in UTC, and the calculator shows today's day of year, its YYDDD and YYYYDDD codes, and the astronomical Julian Date. The day of year changes at midnight UTC, which can be a different date from where you are.
How do I read a Julian date code like 26279?+
The first two digits are the year and the last three the day of that year. 26279 is day 279 of 2026, which is Tuesday, October 6, 2026. Choose YYDDD, enter the code and the calculator gives the calendar date, accounting for leap years.
Is a Julian date the same as the Julian calendar?+
No. The Julian calendar is the older Roman calendar that the Gregorian calendar replaced, and this calculator does not convert dates into it. A Julian date in the sense used here is either a day-of-year code or an astronomical day count, both worked out from ordinary Gregorian dates.
Why does the astronomical Julian Day start at noon?+
It was set up for astronomers, who observed at night, so a whole night's observations fall within one Julian Day. Midnight UTC is therefore half a day before the Julian Day Number of that date.
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