Julian Date Converter
Time & DatesConvert calendar Gregorian dates and times into continuous Julian Day (JD), Modified Julian Day (MJD), and day-of-year ordinal dates for astronomy, geodesy, and satellite tracking.
Modified Julian Date (MJD): 61,286.5
About this calculator
Astronomers, satellite tracking operators, and geodesy researchers use the Julian Day system—a continuous count of days and fractions since noon Universal Time on January 1, 4713 BC—to avoid the complications of irregular month lengths and historical leap year calendar reforms.
This calculator converts any Gregorian calendar date and UTC time into standard Julian Date (JD) and Modified Julian Date (MJD = JD - 2,400,000.5), as well as standard ordinal day-of-year (DOY).
How It Works & Formula
Calculates Julian Day Number using the standard astronomical algorithm: JD = 367·Y - floor(7(Y + floor((M+9)/12))/4) - floor(3(floor((Y + (M-9)/7)/100) + 1)/4) + floor(275M/9) + D + 1721028.5 + (UT hours / 24).
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