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Modified Julian Date Calculator

Enter a calendar date to get its Modified Julian Date and full Julian Date.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

The Julian Date (JD) is a continuous day count astronomers use instead of the calendar, counting from noon UT on January 1, 4713 BC — a system chosen precisely so it never resets and never has to deal with months, leap years, or calendar reforms. The Modified Julian Date (MJD) is JD minus 2,400,000.5, which both shortens the huge JD number and shifts the day boundary to midnight, making MJD = 0 correspond to November 17, 1858.

MJD is the standard timestamp in astronomy, satellite operations, and GPS/GNSS systems, where it's far more convenient than calendar dates for computing time intervals and orbital calculations — it's used, for instance, in satellite ephemeris data and by observatories logging observation times.

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