What week is it?
Today’s week number, and the week number of any date — shown in both counting systems, because “week 1” does not mean the same thing everywhere.
The short answer: under ISO 8601 — the system used by most of Europe and by international business — weeks start on Monday, and week 1 is the week containing the year’s first Thursday. Under the US convention, weeks start on Sunday, and week 1 is simply the week containing January 1. Both are honest ways to count; they just draw the lines in different places, so the same day can carry two different week numbers.
The two systems at a glance
| ISO 8601 | US convention (as defined on this site) | |
|---|---|---|
| Week starts | Monday | Sunday |
| Week 1 is… | The week with the year’s first Thursday (equivalently, the week containing January 4) | The week containing January 1, whatever weekday it falls on |
| Year a week belongs to | The year of that week’s Thursday — late-December days can belong to next year’s week 1, and early-January days to last year’s week 52 or 53 | The year whose January 1 falls in (or starts) the week |
| Weeks in a year | 52 or 53 | 52 or 53 |
| Used by | Most of Europe, international standards, logistics and manufacturing planning | Everyday US calendars and planners |
There is no single official US federal standard for week numbering; the definition above is the common calendar convention, and it is the one this site uses everywhere. Other tools may count US weeks differently — see US vs ISO week numbers.
Common questions
What week are we in right now?
The big number at the top of this page is the current ISO week, worked out from today’s date on your own device. The current week page shows the same answer with this week’s full Monday-to-Sunday span and the weeks either side.
Why does January 1 sometimes fall in week 52 or 53?
Because an ISO week belongs to the year that contains its Thursday. If January 1 is a Friday, Saturday or Sunday, its Thursday still lies in the old year — so those first days of January are numbered as the last week of the previous ISO year. January 1, 2023 was a Sunday, and it belonged to ISO week 52 of 2022.
How many weeks are in 2026?
2026 has 53 ISO weeks — it is a “long year”, because it begins on a Thursday. 2027 goes back to 52. See the full 2026 week calendar or the list of years with 53 weeks.
Which system should I use?
If a document, contract or European partner says “week 34”, it almost certainly means ISO. If you are reading a US wall calendar, the Sunday-start count is what is printed. When it matters, say which system you mean — or give the Monday’s date, which nobody can argue with.