How to Find the Week Number
This tool instantly tells you the week of the year for any date, following the international standard.
- 1. Select a Date: Use the date picker to choose any day, month, and year.
- 2. View the Result: The calculator will immediately show you the correct week number and the year to which that week belongs.
Frequently Asked Questions
What is the ISO 8601 week numbering standard?
This calculator uses the ISO 8601 standard, which is the internationally accepted method for numbering weeks. In this system:
- Weeks start on a Monday and end on a Sunday.
- Week 1 of any year is the first week that contains a Thursday.
- Because of these rules, the first few days of January may belong to the last week of the previous year, and the last few days of December may belong to Week 1 of the following year.
Why is this standard used?
The ISO 8601 standard is used globally in business, finance, and government to avoid ambiguity. Because different regions start their weeks on different days (e.g., Sunday in the US, Monday in Europe), having a single, clear standard ensures that "Week 25" means the same thing to everyone, everywhere.
Is this different from the US week number system?
Yes. In the United States, it is more common to consider Week 1 as the week containing January 1st, and weeks often start on Sunday. This can lead to different week numbers compared to the ISO standard. Our calculator strictly follows the ISO 8601 standard for international consistency.