Julian Date Calculator
Enter a Gregorian date to calculate its Julian Day Number.
Julian Day Numbers provide a continuous count of days that is useful in astronomy, historical calculations and date conversion. This calculator returns the Julian Day Number for the selected Gregorian date at midnight UTC.
Choose a Gregorian calendar date and calculate its corresponding Julian Day Number.
Enter the values you want to compare or calculate, then use the result as a practical reference. The calculator runs in your browser and does not require an account.
This tool also fits into a wider set of practical utilities. Depending on what you are trying to calculate or measure next, you can continue with Day of the Week Calculator, Week Number Calculator, Days Between Dates Calculator and Date Difference Calculator. For the complete collection, visit the utility tools homepage and choose another tool when your task changes.
How to use this calculator
- Enter your values. Select the dates or numbers required by the calculator.
- Check the inputs. Make sure the dates are in the order and range you intend to calculate.
- Calculate the result. The result appears instantly in the calculator above without submitting a form.
- Use the result. Apply the result to your schedule, deadline, planning or date calculation.
How the calculation works
Enter the values you want to compare or calculate, then use the result as a practical reference. The calculator runs in your browser and does not require an account. The calculation is performed locally in your browser, so the page can return a result immediately after you change the inputs.
Things to know about date calculations
Calendar calculations can differ depending on whether a result is treated as an elapsed interval or an inclusive count. This site uses clear calendar-date rules and explains important assumptions where they affect the result. Business-day calculations on this page exclude weekends but do not automatically remove public holidays.
Frequently asked questions
What is a Julian Day Number?
A Julian Day Number is a continuous count of days used to represent dates independently of the ordinary calendar month and year structure.
Is Julian date the same as the Julian calendar?
No. A Julian Day Number is a numerical date system; the Julian calendar is a historical calendar system.