Day of Year / Julian Date
Find out which numbered day of the year any date falls on — day 1 is January 1st, and the total is 365 or 366 depending on leap years.
Referring to a date by its position in the year — "day 214" rather than "August 2nd" — is a format most people never need until they run into a system that actually uses it, at which point it becomes suddenly important to convert correctly. Some data formats, scientific logging systems, and older software store dates this way specifically because a single sequential number is easier to compare and sort programmatically than a month-and-day pair.
The conversion itself sounds like it should be simple counting, and it is, right up until leap years enter the picture — a date in late 2020 (a leap year) and the same calendar date in 2021 (not a leap year) land on different day-of-year numbers once you're past February, because 2020 had an extra day inserted earlier in the year. Getting that off-by-one right by manual counting is exactly the kind of small, easy-to-miss detail this tool exists to handle automatically.
Enter any date, and it returns both the day-of-year number and the total days in that year (365 or 366), so you can immediately see how far through the year that date falls, correctly accounting for whether it's a leap year.
- Pick a date.
- Press Calculate.
- See the day number, out of 365 or 366 for that year.
In this context, 'day of year' (sometimes casually called Julian date) means the sequential day number within a calendar year, not the astronomical Julian Day Number used in astronomy.
Yes — the total shown automatically adjusts to 366 for leap years.