Day of the year
Which day of the year it is, written the way ISO 8601 writes it — and the astronomical Julian Day Number beside it, because those two get confused. Nothing you type here leaves your browser — it is worked out on your own device, so there is nothing to send and nothing to log.
The ordinal date is half of ISO 8601
Everybody knows the
2024-06-15 half. The other half is
2024-167 — year and day number, zero-padded to
three digits. Aviation, the military and a good deal of scientific
data use it, because it sorts correctly and cannot be misread as
month-day or day-month.
It is not a “Julian date”
The day-of-year number is very widely called a Julian date, and that is a different thing. A real Julian Day Number counts days continuously from 1 January 4713 BC and is used in astronomy; today's is over 2.4 million. What people usually mean by “Julian date” on a factory date code is the ordinal date, sometimes with a single-digit year in front, which is ambiguous every ten years. Both are shown here so there is no doubt which you are looking at.
Quarters do not have equal days
Q1 is 90 days (91 in a leap year), Q2 is 91, Q3 and Q4 are 92 each. So a business comparing “revenue per day” across quarters and dividing by 91 every time is wrong in three of them. The difference between Q1 and Q4 is 2.2% — small, and bigger than plenty of numbers people act on.
What it will not do
- It will not decode a manufacturer's date code. Those use dozens of private schemes — that is the date code decoder.
- It will not give you the ISO week. That belongs to a different year from the date about a quarter of the time, which is enough of a trap to deserve its own page — the week number calculator.
- It will not use any calendar but the proleptic Gregorian one.