Julian Date for January 21, 2024

How 2024021 is built

A Julian date in the day-of-year sense is just the year followed by the day number, counted from 1 January. January 21, 2024 is the 21st day of 2024, so the code is 2024 + 021 = 2024021. Many systems drop the century and print 24021 instead.

2024 is a leap year with 366 days, so day numbers run from 001 to 366. After January 21, 2024 there are 345 days left in the year.

Careful: 24021 does not name a century

The 5-digit form 24021 only carries two digits of year, so on its own it is ambiguous. Day 21 of a year ending in 24 could equally be:

• January 21, 2024 — the usual reading for a recent product code
• January 21, 1924
• January 21, 2124

If you are reading a code off packaging, the surrounding context — a shelf life of months rather than decades — almost always settles it.

Day 21 in nearby years

The same day number lands on a different calendar date depending on whether the year is a leap year. This is the single most common mistake when decoding a code whose year you had to guess.

Astronomical Julian Date for January 21, 2024

In astronomy, "Julian Date" means something different: a continuous count of days since noon on 1 January 4713 BC. The Julian Day Number for January 21, 2024 is 2460331 — that number covers the 24 hours from noon UTC on January 21, 2024 to noon UTC the next day.

• JD at 00:00 UTC — 2460330.5
• JD at 12:00 UTC — 2460331.0
• Modified Julian Date (MJD) at 00:00 UTC — 60330.0

See Julian Day for where the count comes from, or the astronomical converter to include a time of day.

Look something else up

• Convert any date — both meanings at once
• Decode a code like 2024021 back to a date
• Every date in January 2024
• Printable 2024 Julian date calendar
• Today's Julian date