What week is it?
- The big number is the current week number, with the Monday-to-Sunday dates of this week and the number of weeks in the year.
- Pick any date to find its week number, or switch to the US system.
- Scroll down for a table of every week of the year with its start and end dates; the selected week is highlighted.
ISO 8601 week numbers
Most of Europe and much of the business world use the ISO 8601 standard: weeks start on Monday, and week 1 is the week that contains the first Thursday of the year (equivalently, the week containing 4 January). Because of that rule, 1–3 January can belong to the last week of the previous year, and 29–31 December can belong to week 1 of the next. ISO years have 52 or 53 weeks; a year has 53 weeks when it starts on a Thursday, or on a Wednesday in a leap year. 2026 is one of them, so 1 January 2027 falls in week 53 of 2026.
US week numbers
In the United States, calendars and many programs count weeks from Sunday, and the week containing 1 January is always week 1, so the last week can be partial. This gives different numbers from ISO for some dates, which is a common source of confusion in international teams. Excel's WEEKNUM uses the US system by default, while ISOWEEKNUM uses ISO 8601.
The page uses your device's date and does all calculations locally.
What week number is it today?
It is shown at the top of the page and updates automatically each day.
How many weeks are in a year?
52 or 53 in the ISO system. The page shows the count for the selected year.
Why does my calendar show a different week number?
It probably uses the US system (Sunday start). Switch the numbering above to compare.