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Week Number Calculator
Find the ISO week number for any date.
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Frequently asked questions
What does "Weeks Left" account for?
It subtracts the selected date's ISO week from that year's actual final ISO week — determined via December 28, which always falls in the last ISO week — since some years have 53 ISO weeks instead of 52.
Why might the week number seem "off" compared to a regular calendar?
This uses the ISO 8601 standard, where weeks start on Monday and week 1 is the week containing the year's first Thursday — so late-December or early-January dates can belong to a week number from the adjacent year.
What does "Day of Year" show?
The 1-based day count from January 1st of that year up to the selected date.
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