The current ISO week number, and a lookup for any other date.
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This page uses the ISO 8601 week system, the one used across Europe and by most calendars and payroll systems: weeks start on Monday, and week 1 is the week containing the first Thursday of the year. That means January 1 can belong to week 52 or 53 of the previous year, and December 29 to 31 can belong to week 1 of the next. A year has 52 or 53 ISO weeks. In the US calendars often count differently (weeks start on Sunday, and week 1 contains January 1), so numbers can differ by one.
What week is it now? The number is shown in the big line above and updates every day.
How many weeks are in a year? An ISO year has 52 or 53 weeks. A calendar year has 52.18 weeks on average (365.25 / 7).
Which day does the week start on? Monday in the ISO system used here.
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