Week Number Calculator – Find the Week Number for Any Date
Week number calculator tells you the week number for any date according to ISO 8601 standard. Enter a date to get the week number and the first and last day of that week.
The tool also shows current week number and displays the year's week sequence in calendar view. Perfect for project management, billing, and scheduling.
What Day Does the International Week Start?
According to ISO 8601 standard and international practice, the week starts on Monday. Week 1 is the week containing the first Thursday of the year (or January 4th). This means Christmas can belong to either the last week of the old year or first week of the new year. In the USA, weeks start on Sunday — this difference can cause confusion in international communication.
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Browse all tools →The week number calculator tells you the week number for any date and the current week number. A simple and quick tool for working with schedules and calendars.
Enter a date or see the current week number – the calculator shows the ISO standard week number.
- See the current week number immediately.
- Find out the week number for any date.
- Calculate which date is the Monday of a specific week.
Week numbering follows the ISO 8601 standard, where the week starts on Monday.
- A year has 52 or 53 weeks – check the weeks around New Year.
- Week 1 is the week containing the first Thursday of the year.
- Week numbers are commonly used in Nordic countries, but not in many other countries.
Week numbers make scheduling and communication easier, especially in work environments.
- In the USA, the week numbering system differs from European – weeks may start on Sunday.
- Calendar applications may display week numbers differently depending on settings.
- The tool works in your browser – your data is not stored.