Julian Day Calculator - Free, Instant, In Your Browser
Enter a date to get its Julian Day Number (used in astronomy and some scientific calendars) and its ISO 8601 week number.
How to use Julian Day Calculator
- 1Enter the required date(s) and details above.
- 2Click Calculate - Julian Day Calculator runs instantly, right in your browser.
- 3Read your result below.
Your file is only processed temporarily for the conversion and is automatically deleted within 24 hours.
Frequently Asked Questions
What is a Julian Day Number?
It's a continuous count of days since a fixed reference point (noon UTC, January 1, 4713 BCE), widely used in astronomy to simplify date math.
What is an ISO week number?
It's the week number under the ISO 8601 standard, where week 1 is the week containing the year's first Thursday and weeks run Monday to Sunday.