Find the ISO week number for any date or see which dates fall in a specific week of the year.
Uses the internationally recognized ISO 8601 week date system for accurate week numbering.
Easily navigate between weeks with next/previous buttons and jump to current week instantly.
See week ranges, day of year, quarter, and other useful calendar information for any date.
ISO 8601 is an international standard for date and time representation. In this system, weeks start on Monday, and Week 1 is the first week with a Thursday. A year can have 52 or 53 weeks.
A year has 53 weeks if January 1st falls on a Thursday, or if it's a leap year and January 1st falls on a Wednesday. This happens approximately every 5-6 years.
Week numbers are commonly used in business, project management, and scheduling. They provide a standardized way to reference specific weeks across different countries and time zones.
Yes! In the ISO system, the last few days of December can belong to Week 1 of the next year if they fall after the last Thursday of December.