Week Number
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About ISO Week Numbers
The ISO 8601 standard defines week numbering used internationally. Each week starts on Monday and ends on Sunday. Week 1 is the week containing the first Thursday of the year.
Because of this rule, dates near the start or end of a calendar year may belong to a different ISO year. For example, January 1st might fall in week 52 or 53 of the previous year, and late December dates can belong to week 1 of the next year.
Week numbers are commonly used in business planning, project management, and scheduling across Europe and many international organizations.