Week to Date
Convert ISO 8601 week-year and week number to Monday–Sunday dates, or look up the ISO week for any calendar date.
Convert ISO week numbers to calendar dates
ISO 8601 labels weeks as YYYY-Www where week 1 is the first week with
at least four days in the new year and weeks start on Monday. This converter works both ways:
enter a calendar date to see its ISO week-year and week number, or enter a week-year and week
to list Monday through Sunday dates.
When teams need ISO weeks
Sprint reporting, manufacturing lots, and European business calendars often reference ISO weeks
instead of month names. Mapping 2026-W01 to exact dates prevents off-by-one errors
around January and December boundaries.
See also Find Week of Year, Week Calculator, and Week of Month Finder.
Frequently Asked Questions
What is the ISO week-year?
It can differ from the calendar year near January and December when a week belongs mostly to an adjacent year. The tool displays the ISO week-year returned by the algorithm.
How many weeks can a year have?
Most years have 52 ISO weeks; some have 53. Invalid week numbers for a given year show an error instead of silent drift.
Which timezone is used?
Dates are local calendar days without a time component, matching typical ISO week date pickers.
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