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What week is any date?

Pick any date below and we'll show you its calendar week number, the day of the week, and the full Monday–Sunday range it falls in.

Date:

How the ISO week is calculated

Under ISO 8601, a week always runs Monday–Sunday, and week 1 of a year is the week containing the year's first Thursday (equivalently, the week containing 4 January). That means a date in early January can belong to the previous year's last week, and a date in late December can belong to the next year's week 1 — which is why the result above shows the ISO week year, not just the calendar year.

Other tools you may want

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• Download 2026 week numbers (.ics) for Outlook, Apple Calendar or Google Calendar
• Printable 2026 calendar with week numbers