Week Number Calculator
Find the ISO week number, day of the year, and weekday for any date. ISO week numbering starts on Monday and is used in planning, payroll, and project management.
Defaults to today.
Week & day of year
Week 22
ISO week 22 of 2026 (week starts on Monday).
- Day of year
- 151 of 365
- Days left in year
- 214
- Day of week
- Sunday
- Year
- 2026
- Leap year?
- No
Frequently asked questions
Which week numbering does this use?
ISO 8601. Weeks start on Monday, and week 1 is the week containing the year's first Thursday.
Why does my week number sometimes show a different year?
ISO weeks at the start or end of a year can belong to the previous or next year. We show the ISO year alongside the week number.
What is the day of year?
The day number within the year, from 1 (Jan 1) to 365 or 366 (Dec 31 in leap years).
Does this work for past dates?
Yes. Pick any date — past, present, or future — and the calculator returns its ISO week and day of year.