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ISO 8601 week

ISO 8601

Week Number

Find the ISO week number and ISO week-year for a selected calendar date.

ISO 8601 week number

Week 372026 · MondayISO weeks start on Monday; week 1 contains the year’s first Thursday.

How ISO weeks work

ISO weeks start on Monday. Week 1 is the week containing the year's first Thursday, so late-December dates can belong to week 1 of the next ISO year.

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