Week Number Calculator
Find the ISO week number for any date.
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Find the ISO week number
Week numbers are common in planning, manufacturing, reporting and European calendars. Choose a date and this calculator returns the ISO week number, ISO year and ISO weekday. The ISO year can differ from the calendar year for dates near New Year.
Why ISO weeks can surprise you
ISO week 1 is the week with the first Thursday of the year. That means early January can belong to the last ISO week of the previous year, and late December can belong to week 1 of the next ISO year.
Frequently asked questions
What is ISO week 1?
It is the week containing the first Thursday of the ISO year.
Why is the ISO year different?
Dates near New Year may belong to the previous or next ISO week-year.
Does this use local time?
The selected date is interpreted as a local calendar date.