ISO Week Number Calculator
Find the ISO week year, week number and Monday-to-Sunday range for a date.
ISO weeks start on Monday. Week 1 contains the first Thursday of the year, so the week year can differ from the date year.
How to use
Choose a calendar date or select Use today.
Read its ISO week year and week number.
Check the start and end dates of that week.
FAQ
How do I use this tool?
Choose a calendar date or select Use today. Read its ISO week year and week number. Check the start and end dates of that week.
When does ISO week 1 begin?
ISO weeks start on Monday. Week 1 is the week that contains the year’s first Thursday.
Why can the week year differ from the calendar year?
A date near New Year can belong to the final ISO week of the previous year or the first ISO week of the next year.
Are my inputs uploaded?
Tool inputs are processed in your browser. Advertising makes separate requests as described in the privacy policy.