Day of Year Calculator
Find the day of the year, ISO week number and year-progress percentage for any date.
Day of Year
Find the day-of-year, ISO week number, and how much of the year has passed.
About the Day of Year Calculator
Pick any date. OmniWhen returns its day of the year (1–366), ISO week number (1–53), day of the week, days remaining in the year, and what percentage of the year has passed.
Useful for project planning, end-of-year reporting, or astronomy calculations.
How it works
Day of year = (your date) − (Jan 1 of the same year), plus 1. ISO week of year is computed by finding the Thursday of the week your date falls in, then dividing by 7 from the year's first Thursday — week 1 always contains January 4 by ISO convention.
Examples
- Mar 1, 2026DOY 60 · ISO week 9 · Year 16% complete
- Dec 31, 2026DOY 365 · ISO week 53
- Jan 1, 2024 (leap year)DOY 1 · 366 days in year
Frequently asked questions
Does day of year start at 1 or 0?
Day 1 is January 1. Day 365 (or 366 in leap years) is December 31.
How does ISO week numbering work?
Weeks start on Monday. Week 1 is the week containing the year's first Thursday (and always contains Jan 4). Some years have 53 ISO weeks.
Why does my date show ISO week 53 / week 1 in early January?
Late December may belong to ISO week 1 of the next year, and early January may belong to ISO week 52 or 53 of the previous year. ISO weeks don't care about calendar-year boundaries.