What Week Is It? (ISO Week Number)
Find the current ISO 8601 week number, or the week number of any date, with the week’s start and end dates and weeks left in the year.
Runs on your device
Result
Results appear here as you type.
What it does
Many businesses, schools and planners in Europe use ISO week numbers: weeks start on Monday and week 1 contains the year’s first Thursday. Leave the date empty for today.
How to use it
- Leave the date blank for today, or choose a date.
- Read the week number and date range.
- Copy it into your planner or report.
Example
31 December 2026 is in ISO week 53 of 2026. Select Try an example above to see it.
When it helps
- Production and delivery planning.
- School timetables and sprints.
- Filing weekly reports.
Questions
Why can 31 December be in week 1?
ISO weeks belong to the year that contains their Thursday, so the last days of December sometimes fall in week 1 of the next year.
Does the US use ISO weeks?
Not usually. US calendars often start weeks on Sunday. This tool uses the ISO standard.
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