Day of Year Calculator
Find the ordinal day number for any date, or the date for a given day number.
How day-of-year numbering works
January 1 is day 1. Each date after that adds one, so December 31 is day 365 in a normal year, or day 366 in a leap year, since February then has 29 days instead of 28. This ordinal count is sometimes called the Julian day number in scheduling and manufacturing contexts, though that name also refers to an unrelated astronomical numbering system, so "day of year" is the less ambiguous term.
Worked examples
February 29, 2024: a leap day, this is day 60 of 2024.
December 31, 2024: day 366, the last day of a 366-day leap year.
December 31, 2025: day 365, the last day of a normal 365-day year.
Common questions
In a normal year, day 100 is April 10. In a leap year it is April 9, because the extra day in February shifts every later date one day earlier in the count.
A 3-digit day number plus the year is shorter and sorts more easily than a full calendar date, which is useful on packaging, batch codes and log files where space is limited.
No, despite the similar name. Astronomical Julian day numbers count continuously from a fixed point thousands of years ago and do not reset each January 1. This calculator uses the everyday "day of the current year" meaning.
Yes. Use the second calculator above: enter the year and the day number and it returns the matching date.