🗓️Julian Date Converter

About this tool

Pick a calendar date, or press Today, to see its day of the year, the YYDDD and YYYYDDD codes, the ISO week, the astronomical Julian Date and the Modified Julian Date. In the second panel, type a Julian code such as 26285, 2026285 or 2026-285 to get the calendar date and weekday.

The two meanings of Julian date

"Julian date" is used for two different things. In manufacturing, food packaging, the military, logistics and older computer systems it usually means an ordinal date: the year followed by the day number within the year, from 001 on 1 January to 365, or 366 in a leap year. Written as YYDDD, 26285 means the 285th day of 2026, which is 12 October; the longer YYYYDDD form, 2026285, avoids ambiguity about the century, and the ISO 8601 standard writes it 2026-285. Batch and "packed on" codes on food, medicines and cosmetics often use this format, sometimes with extra letters or digits for the factory or production line, so check the manufacturer's key. Astronomers mean something else: the Julian Date is a continuous count of days since noon Universal Time on 1 January 4713 BC on the Julian calendar, which makes it easy to calculate the interval between observations without worrying about months or leap years. At midnight UTC on 1 January 2000 the Julian Date was 2,451,544.5. Because it starts at noon and has many digits, the Modified Julian Date subtracts 2,400,000.5, so it begins at midnight and is shorter. Neither meaning refers to dates on the old Julian calendar used before the Gregorian reform. Honest limits: two-digit years are read as 1969 to 2068, a common convention, and some manufacturers use their own codes. The calendar converter shows the Julian calendar, the day of the week calculator finds weekdays and the date calculator counts days.

Frequently asked questions