Week Number Calculator

This gives the ISO 8601 week number for a date, and works the other way too: enter a year and a week number and you get the Monday to Sunday dates that week covers. ISO weeks start on Monday and week 1 is the week holding the first Thursday of January, so the days either side of New Year often belong to the neighbouring year's numbering. The results name that week-numbering year explicitly, and say whether the year runs to 52 or 53 weeks. Sunday-start numbering, used informally in North America, can differ by a week, so check which one your payroll or spreadsheet means.