Julian Day to Gregorian Date Converter

Enter a Julian Day (JD) to convert it to a Gregorian calendar date, time (UTC), weekday, and Modified Julian Day (MJD).

Input

Enter a Julian Day (JD) to convert it to a Gregorian calendar date and time (UTC). The weekday and Modified Julian Day (MJD) are also shown.

Julian Day (JD)

days

Example: 2451545.0 is noon (UTC) on January 1, 2000. The fractional part represents the time of day.

Result

Gregorian date and time

2000-01-01

12:00:00UTC

Weekday

Saturday

Modified Julian Day (MJD)

51,544.5

Day of year

1 th day

The year, month, and day come from the integer part of JD + 0.5, and the time comes from its fractional part. Times are in UTC, and the weekday is derived from JDN modulo 7. Results are correct from the Gregorian reform (1582) onward.

How it works

The Julian Day (JD) is a continuous count of days since noon (UTC) on January 1, 4713 BC. Because each day begins at noon, JD = 0.0 is noon and JD = 0.5 is midnight.
Conversion steps: take JD + 0.5, then split it into its integer part JDN and fractional part F. The integer part yields the year, month, and day; the fractional part yields the hours, minutes, and seconds. A Gregorian reform correction is included, so results are correct for dates from the reform (1582) onward.
The Modified Julian Day (MJD) is defined as MJD = JD minus 2400000.5, shifting the day boundary to midnight.
The weekday is derived from JDN modulo 7 (a remainder of 0 corresponds to Monday). The day of year is the sequential number with January 1 as day 1.
Times are shown in Coordinated Universal Time (UTC). For values before the reform (small JD), results differ from the Julian calendar.

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