ISO Week Number Calculator

Pick a date to see ISO week number, year-week label, and the week start and end dates.

—Week number
—Year-week
—Week start
—Week end

How to use

  1. Select or enter a date.
  2. See the ISO week number and year-week label.
  3. View week start (Monday) and week end (Sunday) dates.

Frequently asked questions

What is ISO week numbering?

Weeks start on Monday. Week 1 is the first week with at least 4 days in the new year.

Why can week 1 be in the previous year?

ISO weeks near January may belong to the previous or next ISO year depending on the day of week.

How is week start/end calculated?

Week starts Monday 00:00 and ends Sunday 23:59 of that ISO week.

Is my data sent to a server?

No. All calculations happen in your browser.

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