Week Number Calculator

Free week number calculator. Find ISO week numbers for any date. Essential for project planning and business scheduling.

Determine the ISO week number for any date. Week numbers are widely used in business, project management, and scheduling to reference specific weeks without specifying exact dates.

Common use cases

  • Project managers referencing sprint weeks
  • Manufacturing planning production schedules
  • Business analysts creating weekly reports
  • Logistics coordinators scheduling deliveries
  • International teams aligning on week references

How to use

  1. Enter the date you want to check
  2. View the ISO week number (1-53)
  3. See the year the week belongs to (can differ at year boundaries)
  4. View the date range of that week
  5. Navigate to adjacent weeks easily

FAQ

What is an ISO week?

ISO weeks start on Monday and week 1 is the first week with at least 4 days in the new year.

Why do some years have 53 weeks?

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

What about the US week numbering?

The tool uses ISO 8601 standard. US numbering (Sunday start) differs slightly at year boundaries.