Julian Date Converter: Date to Julian Day
This Julian date converter handles the two things people mean by "Julian date". Astronomers use the Julian Day Number, a continuous count of days since January 1, 4713 BC, so a date and time becomes a single number like 2461338.5. Manufacturers, the military and food packaging use an ordinal Julian date code such as 26298 (YYDDD), meaning the 298th day of 2026. Enter a calendar date to get both, or enter a Julian Day or a YYDDD code to get the calendar date back, including the day of the week.
Julian Date Converter
Convert a calendar date to a Julian Day Number, day of year or YYDDD Julian date code, and back.
How to use the Julian Date Converter
- Choose the conversion direction.
- Enter a date, a Julian Day Number or a YYDDD code.
- Read the converted date and every format.
- Copy the code you need.
Julian Day formula
a = ⌊(14 − month) ÷ 12⌋, y = year + 4800 − a, m = month + 12a − 3 · JDN = day + ⌊(153m + 2) ÷ 5⌋ + 365y + ⌊y/4⌋ − ⌊y/100⌋ + ⌊y/400⌋ − 32045
Features
- Julian Day Number (JD) and MJD
- Day of year and YYDDD / YYYYDDD codes
- Both directions
- Day of the week
Frequently asked questions
What is today's Julian date?
In YYDDD format it is the 2-digit year plus the day of the year. October 25, 2026 is day 298, so its code is 26298.
What is the Julian Day Number?
A count of days since noon on January 1, 4713 BC, used in astronomy. Noon on January 1, 2000 is JD 2451545.0.
Why does the Julian Day start at noon?
Astronomers chose noon so a whole night of observing falls on one Julian Day. Midnight dates end in .5.
How do I read a Julian date code on food or products?
A code like 26045 means year 2026, day 45, which is February 14. Some makers use 1 digit for the year, like 6045.
Is a Julian date the same as the Julian calendar?
No. The Julian calendar is the old calendar replaced by the Gregorian calendar in 1582. Julian date codes simply count days in the year.