ISO week 21 of 2026 2026When is week 21 of 2026?
Week details
ISO week 21 of 2026 starts on Monday, May 18, 2026 and ends on Sunday, May 24, 2026. The year has 53 ISO weeks, so week 21 is week 21 of 53. The week began 135 days ago. An ISO week always starts on Monday and ends on Sunday. Week 1 is the one that contains the first Thursday of the year, which fixes the count no matter which weekday January 1 falls on. Companies that plan by week number, from shipping to school terms, rely on that consistency so that every planner agrees which dates belong to week 21. Quote a week number instead of a date when the exact day is flexible: deliveries expected in week 21, holidays in week 21, or a sprint review in week 21. Check that everyone uses the same system, because some calendars count Sunday as the first day of the week and number the weeks differently. Where in doubt, confirm with the date range shown here. Week 20 ends on Sunday, May 17, 2026, and week 22 starts on Monday, May 25, 2026. Move through the weeks with the links at the bottom of this page. Today is Wednesday, September 30, 2026. That is day 273 of 365 in 2026, in ISO week 40, with 92 days to go before the year ends. The next dates people plan around are Diwali on Saturday, October 10; Columbus Day on Monday, October 12; Halloween on Saturday, October 31. The moon is a Waning Gibbous tonight, with about 81% of its face lit. All of these figures are recalculated when the page loads, so they always describe the day you open it, not the day the page was published. The Gregorian calendar has twelve months of 28 to 31 days. A normal year has 365 days and a leap year has 366, with the extra day added to February in every year divisible by four except century years that are not divisible by 400. Because 365 is one more than 52 weeks, most dates move forward one weekday each year and two after a leap day. Weeks are numbered under ISO 8601, which starts weeks on Monday and gives week 1 to the week containing the first Thursday of January.Week 21 of 2026
What ISO weeks are
Using week numbers
Nearby weeks
Today's date at a glance
How the calendar works
Monday, May 18, 2026. Sunday, May 24, 2026. 53 ISO weeks. It starts in May. Quarter 2. Monday. It began 135 days ago. ISO week 40 of 2026. Week 20. Week 22. No, only some years do. Yes, use the form above.Frequently asked questions
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