This week
Week 43
The current ISO week runs from Monday, October 19, 2026 through Sunday, October 25, 2026.
Quick reference: October 19 to October 25.
ISO Week Number
The current ISO 8601 week number is 43 of 2026. ISO weeks start on Monday, end on Sunday, and week 1 is the week containing the year's first Thursday.
Current ISO year
ISO week numbering can cross the regular calendar year boundary. Late December dates can fall into week 1 of the next ISO year, and early January dates can belong to the last ISO week of the previous one.
For today, the active ISO year is 2026.
All weeks of 2026
ISO 2026 has 53 weeks, from Dec 29, 2025 to Jan 3, 2027.
W01 Dec 29 – Jan 4
W02 Jan 5 – Jan 11
W03 Jan 12 – Jan 18
W04 Jan 19 – Jan 25
W05 Jan 26 – Feb 1
W06 Feb 2 – Feb 8
W07 Feb 9 – Feb 15
W08 Feb 16 – Feb 22
W09 Feb 23 – Mar 1
W10 Mar 2 – Mar 8
W11 Mar 9 – Mar 15
W12 Mar 16 – Mar 22
W13 Mar 23 – Mar 29
W14 Mar 30 – Apr 5
W15 Apr 6 – Apr 12
W16 Apr 13 – Apr 19
W17 Apr 20 – Apr 26
W18 Apr 27 – May 3
W19 May 4 – May 10
W20 May 11 – May 17
W21 May 18 – May 24
W22 May 25 – May 31
W23 Jun 1 – Jun 7
W24 Jun 8 – Jun 14
W25 Jun 15 – Jun 21
W26 Jun 22 – Jun 28
W27 Jun 29 – Jul 5
W28 Jul 6 – Jul 12
W29 Jul 13 – Jul 19
W30 Jul 20 – Jul 26
W31 Jul 27 – Aug 2
W32 Aug 3 – Aug 9
W33 Aug 10 – Aug 16
W34 Aug 17 – Aug 23
W35 Aug 24 – Aug 30
W36 Aug 31 – Sep 6
W37 Sep 7 – Sep 13
W38 Sep 14 – Sep 20
W39 Sep 21 – Sep 27
W40 Sep 28 – Oct 4
W41 Oct 5 – Oct 11
W42 Oct 12 – Oct 18
W43 Oct 19 – Oct 25
W44 Oct 26 – Nov 1
W45 Nov 2 – Nov 8
W46 Nov 9 – Nov 15
W47 Nov 16 – Nov 22
W48 Nov 23 – Nov 29
W49 Nov 30 – Dec 6
W50 Dec 7 – Dec 13
W51 Dec 14 – Dec 20
W52 Dec 21 – Dec 27
W53 Dec 28 – Jan 3
ISO weeks vs US week numbers
Not every calendar counts weeks the ISO way. US-style calendars (common in the United States and Canada, and in tools like Excel's WEEKNUM by default) start weeks on Sunday and call the week containing 1 January week 1. ISO 8601 — used across most of Europe, by Excel's ISOWEEKNUM and by %V in strftime — starts on Monday and anchors week 1 to the first Thursday.
The two systems often disagree by one: today is ISO week 43 and US week 43. A US year can also have a partial week 53 or 54 that ISO does not, so always say which system you mean in schedules shared across countries — or write the ISO form, e.g. 2026-W43.
How ISO weeks are calculated
Core rules
- Week 1 is the week containing the first Thursday of January.
- Weeks always start on Monday and end on Sunday.
- Every ISO week has exactly 7 days.
- Years can have 52 or 53 ISO weeks.
Why people use them
- Project schedules and manufacturing calendars
- Payroll, accounting, and reporting periods
- Transport, warehousing, and logistics planning
- International teams that work across countries with different local date conventions
How many weeks are in a year?
Most ISO years contain 52 weeks. Some contain 53. A 53-week ISO year happens when January 1 falls on a Thursday, or when it falls on a Wednesday in a leap year.
| ISO year | Weeks | Notes |
|---|---|---|
| 2024 | 52 | Standard 52-week ISO year |
| 2025 | 52 | Standard 52-week ISO year |
| 2026 | 53 | Includes week 53 |
| 2027 | 52 | Standard 52-week ISO year |
| 2028 | 52 | Standard 52-week ISO year |