Year + Day of Year (YYYYDDD)
Days since January 1, 4713 BC
JD - 2,400,000.5
Our Julian date calculator shows you the current day of year (ordinal date), Julian Day Number (JDN), and Modified Julian Date (MJD) in real-time. This tool is essential for anyone working with date calculations in manufacturing, military, aviation, or scientific applications.
The term "Julian date" can refer to several different date formats. The most commonly used in everyday applications is the ordinal date (day of year), while astronomers and scientists typically use the Julian Day Number.
The simplest format counts days from 1 to 365 (or 366 in leap years). January 1st is day 1, December 31st is day 365. This format is widely used in:
The Julian Day Number is a continuous count of days since the beginning of the Julian Period on January 1, 4713 BC (Julian calendar). The day starts at noon UTC, not midnight. This format is used in:
The Modified Julian Date simplifies the JDN by subtracting 2,400,000.5. This creates smaller numbers and shifts the day's start from noon to midnight UTC. It's commonly used in:
To convert a calendar date to its ordinal (day of year) format:
March 15: 31 (Jan) + 28 (Feb) + 15 = Day 74 (or 75 in a leap year)
July 4: 31 + 28 + 31 + 30 + 31 + 30 + 4 = Day 185 (or 186 in a leap year)
December 25: 31 + 28 + 31 + 30 + 31 + 30 + 31 + 31 + 30 + 31 + 30 + 25 = Day 359 (or 360 in a leap year)
Don't confuse the Julian date system with the Julian calendar! The Julian calendar was introduced by Julius Caesar in 46 BC and was the predominant calendar in the Western world until the Gregorian calendar reform in 1582. The Julian Day Number system was named after Julius Scaliger's father, not Julius Caesar.
Convert between Julian dates and calendar dates instantly. Features home screen widgets, date bookmarks, and support for multiple date formats. Perfect for aviation, military, and scientific use.
