ISO week number calculator
Project plans, sprint boards, shipping schedules and payroll often refer to dates by week number. This calculator shows today's week number, finds the week for any date, and lists the dates of any week — Monday to Sunday — using the international ISO 8601 standard that Excel's ISOWEEKNUM and most business software follow. It also tells you whether a year has 52 or 53 weeks.
How to use it
- See this week's number at the top.
- Pick any date to get its week number.
- Or enter a year and week number to get its dates, and open the full list of weeks.
Example
7 October 2026 falls in week 41 (2026-W41), which runs from Monday 5 October to Sunday 11 October. Because 2026 began on a Thursday, it has 53 ISO weeks, and 1 January 2027 still belongs to week 53 of 2026. Need the weekday of a date instead? Use theday of the week finder.
Frequently asked questions
What week number is it today?
The big number at the top of this page is today’s ISO week number, based on your device’s date. Weeks start on Monday, and the week containing the year’s first Thursday is week 1.
Why do some years have 53 weeks?
A year has 52 weeks and 1–2 extra days. When the year starts on a Thursday (or on a Wednesday in a leap year), those extra days make a 53rd ISO week. 2026 is one of these years.
Why can 1 January be in week 52 or 53?
If 1 January falls on a Friday, Saturday or Sunday, it belongs to the last week of the previous year under ISO rules. Likewise, 29–31 December can fall in week 1 of the next year.
Is ISO week numbering used in India?
Many companies, factories, shipping and IT teams in India use ISO weeks (written like 2026-W41) for planning and reporting. Some calendars count weeks from Sunday instead, so check which system your team uses.