What week number is it?
The current ISO 8601 week, the week number of any date, and every week's Monday-to-Sunday dates for a year.
Reading today's date…
How ISO week numbers work
ISO 8601, the international date standard, numbers weeks so every week belongs to exactly one year and every year has 52 or 53 whole weeks. That's why a date's "week-year" can differ from its calendar year around New Year.
The Thursday rule: which week is week 1?
ISO 8601 weeks start on Monday, and week 1 is the week that contains the year's first Thursday (equivalently, the week with 4 January in it). Choose the weekday 1 January falls on:
1 January is a Friday, after Thursday, so those first January days still belong to the last week of the previous year (week 52 or 53). Week 1 starts on the following Monday.
Years that start on a Thursday, and leap years that start on a Wednesday, have 53 ISO weeks.
All weeks in 2026
202653 weeks
| Week | Monday | Sunday |
|---|---|---|
| 1 | Mon 29 Dec 2025 | Sun 4 Jan 2026 |
| 2 | Mon 5 Jan 2026 | Sun 11 Jan 2026 |
| 3 | Mon 12 Jan 2026 | Sun 18 Jan 2026 |
| 4 | Mon 19 Jan 2026 | Sun 25 Jan 2026 |
| 5 | Mon 26 Jan 2026 | Sun 1 Feb 2026 |
| 6 | Mon 2 Feb 2026 | Sun 8 Feb 2026 |
| 7 | Mon 9 Feb 2026 | Sun 15 Feb 2026 |
| 8 | Mon 16 Feb 2026 | Sun 22 Feb 2026 |
| 9 | Mon 23 Feb 2026 | Sun 1 Mar 2026 |
| 10 | Mon 2 Mar 2026 | Sun 8 Mar 2026 |
| 11 | Mon 9 Mar 2026 | Sun 15 Mar 2026 |
| 12 | Mon 16 Mar 2026 | Sun 22 Mar 2026 |
| 13 | Mon 23 Mar 2026 | Sun 29 Mar 2026 |
| 14 | Mon 30 Mar 2026 | Sun 5 Apr 2026 |
| 15 | Mon 6 Apr 2026 | Sun 12 Apr 2026 |
| 16 | Mon 13 Apr 2026 | Sun 19 Apr 2026 |
| 17 | Mon 20 Apr 2026 | Sun 26 Apr 2026 |
| 18 | Mon 27 Apr 2026 | Sun 3 May 2026 |
| 19 | Mon 4 May 2026 | Sun 10 May 2026 |
| 20 | Mon 11 May 2026 | Sun 17 May 2026 |
| 21 | Mon 18 May 2026 | Sun 24 May 2026 |
| 22 | Mon 25 May 2026 | Sun 31 May 2026 |
| 23 | Mon 1 Jun 2026 | Sun 7 Jun 2026 |
| 24 | Mon 8 Jun 2026 | Sun 14 Jun 2026 |
| 25 | Mon 15 Jun 2026 | Sun 21 Jun 2026 |
| 26 | Mon 22 Jun 2026 | Sun 28 Jun 2026 |
| 27 | Mon 29 Jun 2026 | Sun 5 Jul 2026 |
| 28 | Mon 6 Jul 2026 | Sun 12 Jul 2026 |
| 29 | Mon 13 Jul 2026 | Sun 19 Jul 2026 |
| 30 | Mon 20 Jul 2026 | Sun 26 Jul 2026 |
| 31 | Mon 27 Jul 2026 | Sun 2 Aug 2026 |
| 32 | Mon 3 Aug 2026 | Sun 9 Aug 2026 |
| 33 | Mon 10 Aug 2026 | Sun 16 Aug 2026 |
| 34 | Mon 17 Aug 2026 | Sun 23 Aug 2026 |
| 35 | Mon 24 Aug 2026 | Sun 30 Aug 2026 |
| 36 | Mon 31 Aug 2026 | Sun 6 Sep 2026 |
| 37 | Mon 7 Sep 2026 | Sun 13 Sep 2026 |
| 38 | Mon 14 Sep 2026 | Sun 20 Sep 2026 |
| 39 | Mon 21 Sep 2026 | Sun 27 Sep 2026 |
| 40 | Mon 28 Sep 2026 | Sun 4 Oct 2026 |
| 41 | Mon 5 Oct 2026 | Sun 11 Oct 2026 |
| 42 | Mon 12 Oct 2026 | Sun 18 Oct 2026 |
| 43 | Mon 19 Oct 2026 | Sun 25 Oct 2026 |
| 44 | Mon 26 Oct 2026 | Sun 1 Nov 2026 |
| 45 | Mon 2 Nov 2026 | Sun 8 Nov 2026 |
| 46 | Mon 9 Nov 2026 | Sun 15 Nov 2026 |
| 47 | Mon 16 Nov 2026 | Sun 22 Nov 2026 |
| 48 | Mon 23 Nov 2026 | Sun 29 Nov 2026 |
| 49 | Mon 30 Nov 2026 | Sun 6 Dec 2026 |
| 50 | Mon 7 Dec 2026 | Sun 13 Dec 2026 |
| 51 | Mon 14 Dec 2026 | Sun 20 Dec 2026 |
| 52 | Mon 21 Dec 2026 | Sun 27 Dec 2026 |
| 53 | Mon 28 Dec 2026 | Sun 3 Jan 2027 |
Questions people ask
What week number is it today?
The box at the top shows the current ISO 8601 week number for your device's date, with the Monday and Sunday it runs between.
How are ISO week numbers calculated?
Weeks run Monday to Sunday. Week 1 is the week containing the first Thursday of the year, so it can start as early as 29 December or as late as 4 January. To find the week of any date, move to the Thursday of its week, then count which 7-day block of that Thursday's year it falls in.
Why is 1 January sometimes in week 52 or 53?
If 1 January falls on a Friday, Saturday or Sunday, most of that week belongs to the old year, so the whole week is numbered as the old year's last week.
Which years have 53 weeks?
Years that begin on a Thursday, and leap years that begin on a Wednesday. 2026 and 2032 have 53 ISO weeks; 2027 has 52.
Do the US and ISO week numbers differ?
Often. Many US calendars start weeks on Sunday and call the week containing 1 January week 1. Excel's WEEKNUM uses that system by default; use ISOWEEKNUM (or WEEKNUM(date, 21)) for ISO weeks.
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