Julian Date Converter
Separate ordinal dates, ISO week dates and astronomical Julian Day so the overloaded term stays unambiguous. Inputs stay in your browser.
Ordinal date, ISO week date and astronomical Julian Day are shown separately because “Julian date” is ambiguous.
Context matters.
- Astronomical Julian Day begins at noon UTC; midnight therefore ends in .5. This is not the Julian calendar.
Sources & scope
The calculation guide and this source trail show what the result means, where the rule came from and when it was last reviewed. This is source-and-calculation QA, not a claim of medical, legal, tax or other professional review; time-sensitive decisions still belong with the linked authority.
A visible path from input to answer.
Separate ordinal dates, ISO week dates and astronomical Julian Day so the overloaded term stays unambiguous. The page keeps the calculation scope and its limits beside the result so the output can be checked, copied or revisited.
- Read the record. The calculator uses Gregorian date supplied in the form.
- Apply the scope. It applies the Global Gregorian, ISO week-date, ordinal-date and astronomical date notation reference and the explicit date, unit and counting conventions shown in the result.
- Expose the checkpoints. Intermediate rows, warnings and timeline events stay visible; the emphasized row identifies the primary checkpoint when one exists.
Ordinal date, ISO week date and astronomical Julian Day are shown separately because “Julian date” is ambiguous.
- Ordinal date2026-235
Calculation purpose: Separate ordinal dates, ISO week dates and astronomical Julian Day so the overloaded term stays unambiguous. This is a high-sensitivity reference output; the linked authority or qualified professional controls the final decision.
Calendar inputs use plain year-month-day semantics. Leap days, month ends, date-pair order and unsupported dates are checked before the result is shown.
Rule set 1.1.0 · Last reviewed 2026-08-22 · Next review due 2027-02-22. The source panel below contains the linked evidence.
What to know before using the result.
What does Julian date mean here?
The tool distinguishes the continuous astronomical Julian Day from ISO week dates and ordinal day-of-year notation, which are often informally called Julian dates.
What is an ISO week date?
It identifies a date by ISO week-numbering year, week and weekday rather than calendar month and day.
Why can the ISO week year differ from the calendar year?
Dates near New Year can belong to the first or last ISO week of an adjacent week-numbering year.