Calculate the ISO week number for any date. Find the start and end dates of a specific week, determine the total number of weeks in a year, and convert between dates and week numbers instantly.
This calculator uses the ISO 8601 week numbering system, which is the international standard for week numbers. In this system, weeks start on Monday, and the first week of the year is the one that contains the first Thursday. This is widely used in Europe, Asia, and international business contexts for project planning, payroll, and scheduling.