ISO week numbers

ISO 8601 week 1 is the week containing 4 January. Weeks start on Monday. Our calendars keep ISO week numbers even if you print a Sunday-start grid.

• 2025 calendar with week numbers
• 2026 calendar with week numbers
• 2027 calendar with week numbers
• 2028 calendar with week numbers

Look up any date with the week number calculator. The definition is in ISO 8601. More detail is in how ISO week numbers work.