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ISO Week Number

Find the ISO 8601 week number for a date, or the Monday–Sunday range for a given ISO week and year.

ISO Week for a Date

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ISO 8601 weeks start on Monday. Week 1 is the week that contains the first Thursday of the year (equivalently, the week containing January 4).

Enter any date to get its ISO week number and ISO year.

Dates for an ISO Week

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Returns the Monday through Sunday date range for the selected ISO week number and year.

Choose a year and week number to see that week’s date range.

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