Ordinal Date (Day of Year) Calculator
Find the ordinal date — the day-of-year number from 1 to 366 — for any date, with days remaining and the percent of the year elapsed.
How it works
day of year = the date − January 1 of that year + 1 (so Jan 1 = 1) · total days = 366 in a leap year, else 365 · percent elapsed = day of year ÷ total × 100 · ordinal date format is YYYY-DDD
The ordinal date, also called the Julian day-of-year in everyday use, numbers each day sequentially from 1 on January 1 up to 365 or 366 on December 31. It appears in the ISO 8601 YYYY-DDD form and is common in aviation, manufacturing lot codes and scientific data because it needs no month. Leap years reach 366; the tool also reports how many days are left in the year and how much of it has passed.
Worked example
September 15, 2026 is day 258 of 365 (2026 is not a leap year). Written as an ordinal date that is 2026-258, with 107 days remaining and about 70.7% of the year elapsed.
Sources: Ordinal date — Wikipedia
Frequently asked questions
Is the ordinal date the same as a Julian date?
In casual use "Julian date" often means this day-of-year number, which is what this tool gives. Strictly, the astronomical Julian Day is a continuous count of days since 4713 BC — a different, much larger number.
What is the highest day number possible?
366, reached only on December 31 of a leap year. In common years December 31 is day 365, because there is no February 29.
Where is the ordinal date used?
In ISO 8601 dates (YYYY-DDD), aviation and logistics, product date codes, and data logging — anywhere a compact, month-free day index is convenient.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.