Converter
Calendar Date to Julian Date
Enter any month, day and year to get its Julian date — both the day-of-year code used in industry and the astronomical Julian Date used in science.
Convert a calendar date
- Julian Date (JD)
- Modified JD (MJD)
- Julian Day Number
The formula for the day-of-year Julian date
The ordinal Julian date is year followed by the
day of year. The day of year is:
day_of_year = day_of_month + sum(days in all earlier months this year)
For 21 July 2026 that is 21 + (31 + 28 + 31 + 30 + 31 + 30) = 21 + 181 =
202, giving 2026202. See the full
perpetual day-of-year chart for a
printable lookup.
The astronomical Julian Date
For the continuous astronomical count this tool uses the standard algorithm from Jean Meeus, which also accounts for the time of day. Add a UTC time in the input to get the exact fractional Julian Date. Learn more on the Julian Day reference page.
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Frequently asked questions
How do I turn today’s date into a Julian date?
Click "Use today" or enter the month, day and year. The converter shows the day-of-year code (for example 2026202) along with the astronomical Julian Date and MJD.
How is the day of year calculated?
Add up the lengths of all the months before the current one, then add the day of the month. January 1 is day 1. In leap years, any date from March onward is one higher than in a common year because February has 29 days.
What is the difference between the day-of-year code and the astronomical JD?
The day-of-year code restarts at 1 every January. The astronomical Julian Date never restarts — it is a single continuous count of days used in astronomy, currently in the 2,461,000s.