Clocks & Time TOOL
Week calculator
Find the date range and ISO week number.
ISO 8601 · Weeks start on Monday
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Week calculator · How to use
Find the date range and ISO week number.
Example
2026-01-01 → ISO week 1 of 2026
Things to know
ISO weeks start on Monday, with January 4 in week one. The ISO week-year can differ from the calendar year.
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