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Week Number Calculator
Find the ISO 8601 week number for any date.
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What is an ISO week number?
ISO 8601 defines week 1 of a year as the week containing that year's first Thursday — equivalently, the week containing January 4. Weeks run Monday to Sunday. This means the first few days of January can sometimes belong to week 52 or 53 of the previous year, and the last days of December can belong to week 1 of the next year.