What week is it?
Today is selected. Pick any date to see its week number.
What you enter stays on this page and is not sent anywhere.
Week systemUsed in Europe, Asia and most business calendars.
Source, checked October 19, 2026: ISO 8601-1:2019
How to use it
- Pick a date, or press Today.
- Choose ISO weeks (Monday start) or US weeks (Sunday start).
- Read the week number, the dates it covers, and open the list of all weeks.
Questions
What is the difference between ISO and US week numbers?
ISO weeks start on Monday and week 1 is the week with the year's first Thursday. US weeks start on Sunday and week 1 is the week that contains January 1.
Why can January 1 fall in week 52 or 53?
In the ISO system a week belongs to the year that holds most of its days. The first days of January can still be in the last week of the previous year.
Which years have 53 weeks?
In ISO, a year has 53 weeks when January 1 is a Thursday, or a Wednesday in a leap year. 2026 is one of them. Most years have 52.
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