What Week Number Is It?
ISO 8601 week numbers for 2026
Jun 29 – Jul 5
Day 183 of 365 · 182 days left · 2026-W27
All Weeks of 2026
| Week | Start (Monday) | End (Sunday) |
|---|---|---|
| W1 | Dec 29 | Jan 4 |
| W2 | Jan 5 | Jan 11 |
| W3 | Jan 12 | Jan 18 |
| W4 | Jan 19 | Jan 25 |
| W5 | Jan 26 | Feb 1 |
| W6 | Feb 2 | Feb 8 |
| W7 | Feb 9 | Feb 15 |
| W8 | Feb 16 | Feb 22 |
| W9 | 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 |
Understanding ISO Week Numbers
ISO 8601 defines a standardized week numbering system used internationally in business, government, and computing. Under this standard, weeks always start on Monday and end on Sunday. Week 1 is defined as the week containing the first Thursday of January — equivalently, the week containing January 4th.
This definition means that a year's first few days (January 1–3) may belong to the last week of the previous year if they fall before the first Thursday. Similarly, the last few days of December may belong to week 1 of the following year. Most years have 52 ISO weeks, but roughly one in every five or six years has 53 weeks.
The ISO week date format writes dates as YYYY-Www-D. For example, 2026-W15-1 represents Monday of week 15 of 2026. This notation is widely used in manufacturing (production planning), logistics (shipping schedules), and software development (sprint planning).
Frequently Asked Questions
What week number is it now?
The current ISO week number is shown at the top of this page — it is calculated live in your browser, so it is always up to date. ISO weeks run from Monday to Sunday.
How are ISO week numbers calculated?
ISO 8601 defines week 1 as the week containing the first Thursday of January. Weeks always start on Monday and end on Sunday. This means that January 1 can fall in week 52 or 53 of the previous year, and December 31 can fall in week 1 of the following year.
How many weeks are in a year?
Most years have 52 ISO weeks. Some years have 53 weeks — this happens when January 1st falls on a Thursday, or when it falls on a Wednesday in a leap year. These "long years" occur roughly every 5-6 years.
Why do weeks start on Monday?
The ISO 8601 standard defines Monday as the first day of the week. This is the most widely used convention internationally and is required for consistent ISO week numbering. Some countries (like the US) traditionally use Sunday as the first day, but ISO week numbers always use Monday.
What is the ISO 8601 week date format?
The ISO week date notation writes dates as YYYY-Www — for example, 2026-W15 is week 15 of 2026. A day can be appended as YYYY-Www-D where D is 1 (Monday) through 7 (Sunday).