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Julian Date Converter

Convert a calendar date to a Julian Day Number, Modified Julian Date and ordinal (YYDDD) date.

About the Julian Date Converter

Enter a date and time (UTC). The calculator gives the astronomers' Julian Day, the Modified Julian Date and the ordinal date (year and day of year) used in industry.

Astronomers count days continuously from noon on 1 January 4713 BC (Julian calendar): the Julian Day. The Modified Julian Date (JD − 2,400,000.5) starts at midnight and is easier to use. Industry and the military often say “Julian date” for the ordinal date, the year plus the day of the year, like 26311.

The formula

JD = days since 1970-01-01 + 2,440,587.5 (+ fraction of the day)

Worked example

1 January 2026 at 12:00 UTC

  1. Julian Day 2,461,042
  2. Modified Julian Date 61,041.5
  3. Ordinal date 2026-001 (short form 26001)

Questions people ask

Why does the Julian Day start at noon?

So astronomers' nights didn't span two dates.

Which “Julian date” do I need?

Food and manufacturing codes use the ordinal YYDDD format; astronomy uses JD.