Week of Year Finder

Free week of year finder. Find the ISO week number (1-53) for any date. Uses international ISO 8601 standard with Monday as week start.

Find the ISO week number for any date. Weeks are numbered 1-53 following the ISO 8601 international standard, where weeks start on Monday and week 1 is the first week with at least 4 days in the new year.

Common use cases

  • Business planning by week number
  • International project coordination
  • Manufacturing and production scheduling
  • Sprint planning in agile development
  • Financial reporting by week

How to use

  1. Select or enter any date
  2. View the ISO week number (1-53)
  3. See which year the week belongs to
  4. Note that weeks at year boundaries may belong to adjacent years
  5. Copy the result for scheduling and planning

FAQ

What is ISO week numbering?

ISO 8601 defines weeks starting Monday. Week 1 is the first week with 4+ days in the new year.

Why do some years have 53 weeks?

Years starting on Thursday (or Wednesday in leap years) have 53 weeks to cover all days.

Can January 1 be in week 52?

Yes, if January 1 falls on Friday, Saturday, or Sunday, it belongs to the previous year's last week.