Current ISO Week
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Week Number Lookup
Enter any date to find its ISO week number, day of year, and week range.
How ISO Week Numbers Work
The ISO 8601 standard defines weeks starting on Monday, numbered 01–52 (or 53). Week 01 is the week containing the first Thursday of January.
Days at the start of January may belong to the last week of the previous year; days at year-end may fall in Week 01 of the next year.
Written as YYYY-Www — e.g. 2026-W08.