What week of the year is it? This week number calculator shows the ISO week number for any date, plus the date range for that week.
Week number calculator
Using the calculator
Select any date to see its ISO week number, the year it belongs to (which can differ at year boundaries), and the Monday-to-Sunday range for that week.
About ISO week numbers
ISO 8601 defines week numbering:
- Weeks start on Monday and end on Sunday
- Week 1 contains January 4 (or the first Thursday of the year)
- Most years have 52 weeks (but some have 53 with the ISO standard!)
- Dec 29-31 may belong to week 1 of the next year
- Jan 1-3 may belong to week 52/53 of the previous year
Years with 53 weeks occur roughly every 5-6 years. For example, 2020 and 2026.
