Julian Day Calculator


Julian Day Number(JD#): Select Calendar AutoSelect (Julian / Gregorian) Use Julian Only

How many days away...

This additional calculation puts a number of days between date one and date two. You can add a number in the field, or change the dates to see how many days between the two.
If this doesn't make sense to you and you are wanting to know the number of days between two different dates, we suggest that you use our simplified Days Between Dates Calculator.
Date 1 is days earlier than date 2


Julian Day Number (JD#): Select Calendar AutoSelect (Julian / Gregorian) Use Julian Only

Julian Day Information

In astronomy, a JD (Julian Date) is defined as the contiguous count of days from January 1, 4713 B.C., Greenwich Mean Noon (equal to zero hours UTC). The fraction of each day is represented as a decimal number. Hence noonGMT) on January 2, 4713 B.C. would have JD# (Julian Date number) 1.00000, 6.00 pm GMT on the same day would have JD# 1.25000 and 6.00 hours Coordinated Universal Time (UCT) would have JD# 2443509.75.
Why was January 1, 4713 B.C. chosen as the starting point? According to most knowledgeable sources on the subject, it is the most recent day (certainly that I can remember...) in which the year began on a Sunday with a full moon. Also day 1 was chosen as January 1, 4713 B.C. because the Julian Calendar, the Lunar Calendar and the Roman Tax Calendar all coincided. This happens every 7,980 years, so the next coincidence will be in 3267 A.D. I'll let you know if it actually happens that way next time...