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The live current ISO week number, the complete calendar of weeks for 2026, 2027 and 2028 with every Monday-to-Sunday range, and a date finder that maps any date to its week number.

Calendar weeks 2026Calendar weeks 2027Calendar weeks 2028

Every week number on this site is computed directly from the ISO-8601 standard, the international convention used for scheduling and business. In that system a week always runs from Monday to Sunday, and week 1 of a year is the week containing the first Thursday of January.

Because the dates are calculated from the standard rather than typed in by hand, the numbers stay consistent from year to year. That is also why the years differ: 2026 is a 53-week ISO year (week 1 starts on Monday, December 29, 2025), while 2027 is a 52-week year (week 1 starts on Monday, January 4, 2027) and 2028 is a 52-week year (week 1 starts on Monday, January 3, 2028).

CalendarWeeks is an independent site. It is free to use, needs no account or sign-up, and is funded by the advertising on its pages. There is no newsletter, no tracking beyond the ads themselves, and no personal data is collected — see the privacy policy for details.

If a date or a week number ever looks wrong, we want to know. Calendar week data is used for planning, sprints and deadlines, so accuracy matters, and reported mistakes are corrected quickly.

Questions, corrections to the calendar data, advertising enquiries and data-protection requests are all welcome.