Julian Day Number Calculator

This JavaScript example calculates the Julian Day Number for any date on the Gregorian or Julian (proleptic) calendars. Enter a date (Month, Day, Year) and compute the Julian Day Number (click radio buttons to switch between calendars). Or, enter a Julian Day Number and find the date. Click reset to try a new date or day number.

Try entering 10/4/1582 on the Julian Calendar: What is the JD? Now enter 10/15/1582 on the Gregorian Calendar: What is the JD? It should be one day later, since Friday, 10/15/1582 (Gregorian) immediately followed Thursday, 10/4/1582 (Julian). Note also that if you switch between Julian and Gregorian, there is a 10-day difference for a given date in 1582.

Warning: This calculator is not guaranteed for Gregorian dates prior to 1582, nor for negative Julian Day Numbers.

Gregorian
Julian

Month	Day	Year		Julian Day Number

You can use the Document Source function in the View menu to look at the source of this HTML document (if you wish). In the source, you'll see various math and formatting functions using the JavaScript language.