Day of Year
Day 206 of 365 (common year)
Day of Year Calculator
Find the ordinal day number (1–366) for any date.
Jan 156.4% through the yearDec 31
ISO 8601 Ordinal Date
YYYY-DDD format used in astronomy, military, and some file naming conventions.
Days Remaining
Days left until Dec 31.
What is Day of Year?
The day of year (also called ordinal date or Julian day number — not to be confused with Julian Date in astronomy) is the sequential day count from January 1 (day 1) to December 31 (day 365 or 366 in leap years). It's used in agriculture, meteorology, military date-time groups, and ISO 8601 ordinal date format (YYYY-DDD).
Leap Years
In a leap year, February has 29 days, making the year 366 days total. This shifts all day numbers from March 1 onward by one compared to common years. A year is a leap year if it's divisible by 4, except centuries (divisible by 100), unless also divisible by 400.
Where Day of Year is Used
ISO 8601 ordinal
YYYY-DDD format (e.g. 2024-197)
Satellite imagery
NASA/NOAA file naming conventions
Manufacturing
Batch/lot date codes on products
Military DTG
Date-time group in operational messages