Parallel Julian / Gregorian Calendar Calculator
For Any Given Date On Either Calendar
PHP Program by Jay Tanner
Calendar Date:   ±Y  M  D   (Neg Year = BC)
Calendar Input Mode:    Julian              Gregorian 
J   2025     May
SunMonTueWedThuFriSat
      1 2 3 4
5 6 7 8 9 10 11
12 13 14 15 16 17 18
19 20 21 22 23 24 25
26 27 28 29 30 31  
G   2025     May
SunMonTueWedThuFriSat
        1 2 3
4 5 6 7 8 9 10
11 12 13 14 15 16 17
18 19 20 21 22 23 24
25 26 27 28 29 30 31
              

 DATE = May 22, 2025 = Thursday on the Gregorian Calendar  

 JD Number = 2460818 on Gregorian calendar  
           = JD (Julian Date) at 12:00:00 on date  

 Julian Calendar Date = Gregorian Calendar Date - 13 days 

 Note that the corresponding days of the week are the same on both 
 calendars no matter the number of days difference between them.