Current Week Number — ISO Week Number Today
See the current ISO week, its Monday-to-Sunday range, and the week-year. Use the yearly table to plan a report or check a future week.
Week Number
Use the current week number, compare ISO and US systems, and move into adjacent business-calendar tools.
Week numbers for 2026
Use the full-year table when you need a reference chart rather than the live widget at the top of the page.
| Week | Start | End | Even/Odd |
|---|---|---|---|
| W1 | Dec 29 | Jan 4 | Odd |
| W2 | Jan 5 | Jan 11 | Even |
| W3 | Jan 12 | Jan 18 | Odd |
| W4 | Jan 19 | Jan 25 | Even |
| W5 | Jan 26 | Feb 1 | Odd |
| W6 | Feb 2 | Feb 8 | Even |
| W7 | Feb 9 | Feb 15 | Odd |
| W8 | Feb 16 | Feb 22 | Even |
| W9 | Feb 23 | Mar 1 | Odd |
| W10 | Mar 2 | Mar 8 | Even |
| W11 | Mar 9 | Mar 15 | Odd |
| W12 | Mar 16 | Mar 22 | Even |
| W13 | Mar 23 | Mar 29 | Odd |
| W14 | Mar 30 | Apr 5 | Even |
| W15 | Apr 6 | Apr 12 | Odd |
| W16 | Apr 13 | Apr 19 | Even |
| W17 | Apr 20 | Apr 26 | Odd |
| W18 | Apr 27 | May 3 | Even |
| W19 | May 4 | May 10 | Odd |
| W20 | May 11 | May 17 | Even |
| W21 | May 18 | May 24 | Odd |
| W22 | May 25 | May 31 | Even |
| W23 | Jun 1 | Jun 7 | Odd |
| W24 | Jun 8 | Jun 14 | Even |
| W25 | Jun 15 | Jun 21 | Odd |
| W26 | Jun 22 | Jun 28 | Even |
| W27 | Jun 29 | Jul 5 | Odd |
| W28 | Jul 6 | Jul 12 | Even |
| W29 | Jul 13 | Jul 19 | Odd |
| W30 | Jul 20 | Jul 26 | Even |
| W31 | Jul 27 | Aug 2 | Odd |
| W32 | Aug 3 | Aug 9 | Even |
| W33 | Aug 10 | Aug 16 | Odd |
| W34 | Aug 17 | Aug 23 | Even |
| W35 | Aug 24 | Aug 30 | Odd |
| W36 | Aug 31 | Sep 6 | Even |
| W37 | Sep 7 | Sep 13 | Odd |
| W38 | Sep 14 | Sep 20 | Even |
| W39 | Sep 21 | Sep 27 | Odd |
| W40 | Sep 28 | Oct 4 | Even |
| W41 | Oct 5 | Oct 11 | Odd |
| W42 | Oct 12 | Oct 18 | Even |
| W43 | Oct 19 | Oct 25 | Odd |
| W44 | Oct 26 | Nov 1 | Even |
| W45 | Nov 2 | Nov 8 | Odd |
| W46 | Nov 9 | Nov 15 | Even |
| W47 | Nov 16 | Nov 22 | Odd |
| W48 | Nov 23 | Nov 29 | Even |
| W49 | Nov 30 | Dec 6 | Odd |
| W50 | Dec 7 | Dec 13 | Even |
| W51 | Dec 14 | Dec 20 | Odd |
| W52 | Dec 21 | Dec 27 | Even |
| W53 | Dec 28 | Jan 3 | Odd |
ISO 8601 week numbering explained
The ISO 8601 standard defines a consistent system for numbering weeks. Weeks begin on Monday and end on Sunday. Week 1 is the week containing the first Thursday of January, which means it always includes January 4.
This definition keeps the system internationally consistent and avoids the ambiguity of partial first weeks. Most years have 52 ISO weeks, while years that begin on Thursday, or leap years that begin on Wednesday, have 53. 2026 has 53 ISO weeks.
US vs ISO week numbering
The United States often uses a different convention where weeks start on Sunday and Week 1 begins on January 1 no matter what day that falls on. That difference matters most in early January and late December, where ISO and US week numbers can diverge by one full week.
For cross-border business, manufacturing, software, and reporting, ISO week numbering is usually the safer reference because it is explicit and standardised.
Why week numbers matter
Week numbers are common in production schedules, project planning, invoicing, delivery windows, and European business reporting. Even and odd week references are also used in recurring schedules such as waste collection, staff rotations, and academic timetables.
Frequently Asked Questions
What week number is it?
The live widget shows the week number for your local date. ISO weeks run from Monday to Sunday.
Is this an even or odd week?
Even weeks have numbers divisible by 2; odd weeks do not. The live widget identifies the current week type.
How many weeks are in 2026?
2026 has 53 ISO weeks. Most ISO years have 52 weeks, while years that start on Thursday and leap years that start on Wednesday have 53.
When does ISO week 1 start?
ISO week 1 is the week containing the first Thursday of January. It always includes January 4th. Days before that may belong to week 52 or 53 of the previous year.
What is the difference between ISO and US week numbering?
ISO weeks start on Monday and the first week must contain the year's first Thursday. US weeks start on Sunday and Week 1 always starts on January 1. The two systems can differ by up to one week, especially in early January.
Why do Europeans use week numbers?
Week numbers provide a universal, unambiguous way to reference a seven-day period. They are standard in EU business, manufacturing, and government reporting, and are deeply embedded in Scandinavian culture for everyday scheduling.
Related Tools
Continue with adjacent calculators and references that solve the next step.
Use the week-year with the week
The first Thursday decides week one
ISO weeks start on Monday. Week one is the week containing January 4, which is also the week containing the first Thursday of the calendar year. The ISO week-year follows that Thursday.
Near New Year, a date can belong to a different week-year than its calendar year. Label weekly reports with both values, such as 2020-W53. A bare “week 53” is not enough to identify an interval.
A Sunday calendar is a different convention
A Sunday-first display does not automatically define a universal US week-number standard. This site’s US-style comparison assigns week one to the week containing January 1. Payroll, retail, and fiscal systems may choose a different rule.
A 53-week ISO year occurs when January 1 is a Thursday, or when a leap year begins on Wednesday. It is not simply every leap year. Use the year table to check the Monday and Sunday dates of a particular week.
Friday January 1, 2021 belongs to ISO week 2020-W53. Monday January 4, 2021 begins 2021-W01. The calendar year and ISO week-year disagree for those first three days.
A common mistake to avoid
Alternating odd/even week schedules need a rollover policy: week 53 and the following week 1 are both odd.