Week Number Calculator
Get the ISO week number for any date, with week start and end dates.
About ISO Week Numbers
The ISO 8601 week numbering system starts each week on Monday. Week 1 is the week containing the first Thursday of the year (or equivalently, the week containing January 4th).
This means a year can have 52 or 53 weeks, and the first few days of January may belong to the last week of the previous year.
ISO week numbers are widely used in business, project management, and international shipping for standardized date references that avoid ambiguity across countries.
About This Tool
This week number calculator helps you quickly find the ISO week number for any date, along with the exact start and end dates of that week. It's essential for international business, project management, payroll systems, and anywhere standardized weekly references are needed to avoid date ambiguity.