Find the ISO week number of a date
Find the ISO-8601 week number for any date, along with that week's Monday-to-Sunday date range.
Defaults to today, but you can check the week number for any date.
See which numbered week of the year that date falls in.
The ISO year and the Monday-to-Sunday range of that week are shown too.
Frequently asked
What is an ISO week number?
The ISO-8601 standard defines weeks as running Monday to Sunday, with week 1 being the week that contains the year's first Thursday. That's the numbering most calendars and spreadsheets use.
Why does the ISO year sometimes differ from the calendar year?
A date in very early January can fall in the last ISO week of the previous year, and a date in very late December can fall in week 1 of the next year, since ISO weeks always start on a Monday.
Does the year ever have 53 weeks?
Yes. Most years have 52 ISO weeks, but years whose first day (or a leap year's last day) is a Thursday get a 53rd.