Julian day converter

Convert between calendar dates and Julian Day / Modified Julian Day numbers.

Astronomical Julian Day counts days from noon UT, January 1, 4713 BC (proleptic Julian calendar); MJD subtracts 2,400,000.5. The ordinal code (YYDDD) is the packaging 'Julian date'. Dates use the proleptic Gregorian calendar.

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How to use

  1. Enter a date (and optional time) or a JD/MJD number.
  2. Read the matching value.
  3. Copy the result.

What it supports

Gregorian calendar proleptic to all dates; JD is the astronomical day count from noon UT Jan 1, 4713 BC — not the "Julian date" yyddd used in some industries. Dates are interpreted as UTC.

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