Week Number
The current ISO week number, the span of the current week, and a full table of all ISO weeks for the year.
Current ISO week
Today's date
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Week spans
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All Weeks of 2026
| Week | Monday | Sunday |
|---|---|---|
| Wk 1 | Dec 29 | Jan 4 |
| Wk 2 | Jan 5 | Jan 11 |
| Wk 3 | Jan 12 | Jan 18 |
| Wk 4 | Jan 19 | Jan 25 |
| Wk 5 | Jan 26 | Feb 1 |
| Wk 6 | Feb 2 | Feb 8 |
| Wk 7 | Feb 9 | Feb 15 |
| Wk 8 | Feb 16 | Feb 22 |
| Wk 9 | Feb 23 | Mar 1 |
| Wk 10 | Mar 2 | Mar 8 |
| Wk 11 | Mar 9 | Mar 15 |
| Wk 12 | Mar 16 | Mar 22 |
| Wk 13 | Mar 23 | Mar 29 |
| Wk 14 | Mar 30 | Apr 5 |
| Wk 15 | Apr 6 | Apr 12 |
| Wk 16 | Apr 13 | Apr 19 |
| Wk 17 | Apr 20 | Apr 26 |
| Wk 18 | Apr 27 | May 3 |
| Wk 19 | May 4 | May 10 |
| Wk 20 | May 11 | May 17 |
| Wk 21 | May 18 | May 24 |
| Wk 22 | May 25 | May 31 |
| Wk 23 | Jun 1 | Jun 7 |
| Wk 24 | Jun 8 | Jun 14 |
| Wk 25 | Jun 15 | Jun 21 |
| Wk 26 | Jun 22 | Jun 28 |
| Wk 27 | Jun 29 | Jul 5 |
| Wk 28 | Jul 6 | Jul 12 |
| Wk 29 | Jul 13 | Jul 19 |
| Wk 30 | Jul 20 | Jul 26 |
| Wk 31 | Jul 27 | Aug 2 |
| Wk 32 | Aug 3 | Aug 9 |
| Wk 33 | Aug 10 | Aug 16 |
| Wk 34 | Aug 17 | Aug 23 |
| Wk 35 | Aug 24 | Aug 30 |
| Wk 36 | Aug 31 | Sep 6 |
| Wk 37 | Sep 7 | Sep 13 |
| Wk 38 | Sep 14 | Sep 20 |
| Wk 39 | Sep 21 | Sep 27 |
| Wk 40 | Sep 28 | Oct 4 |
| Wk 41 | Oct 5 | Oct 11 |
| Wk 42 | Oct 12 | Oct 18 |
| Wk 43 | Oct 19 | Oct 25 |
| Wk 44 | Oct 26 | Nov 1 |
| Wk 45 | Nov 2 | Nov 8 |
| Wk 46 | Nov 9 | Nov 15 |
| Wk 47 | Nov 16 | Nov 22 |
| Wk 48 | Nov 23 | Nov 29 |
| Wk 49 | Nov 30 | Dec 6 |
| Wk 50 | Dec 7 | Dec 13 |
| Wk 51 | Dec 14 | Dec 20 |
| Wk 52 | Dec 21 | Dec 27 |
| Wk 53 | Dec 28 | Jan 3 |
ISO vs. US Week Numbering
ISO 8601
- Week starts on Monday
- Week 1 = the week with the year's first Thursday
- December dates can fall in Week 1 of the next ISO year
- Used in Europe, Bulgaria, and most Asian countries
US System
- Week starts on Sunday
- Week 1 = the week containing January 1st
- Can result in Week 53 or even Week 54
- Used in the US, Canada, and Australia
Frequently Asked Questions
What is an ISO week number?
ISO week numbers are defined by the ISO 8601 standard. Week 1 of every year is the week that contains the year's first Thursday. Weeks always run Monday through Sunday.
When does ISO Week 1 start?
ISO Week 1 starts on the Monday of the week that contains January 4th. This means the first week can begin as early as December 29th of the previous year. You can find it by locating the year's first Thursday and stepping back to Monday.
How many weeks are in a year?
Most years have 52 ISO weeks. Years where January 1st falls on a Thursday — or Wednesday in a leap year — have 53 ISO weeks. These are called "long" ISO years.
What is the difference between ISO and US week numbering?
ISO 8601 starts weeks on Monday and defines Week 1 as the one containing the first Thursday. The US system starts weeks on Sunday and defines Week 1 as the one containing January 1st. The same date can fall in a different week number depending on which system you use.
Can the last days of December belong to Week 1?
Yes. If December 29, 30, or 31 falls in a week whose Thursday is in January, those days belong to Week 1 of the next ISO year — not to the final week of the current year.