Week Number Calculator
Find the ISO week number for any date.
Week 32ISO Week
2026ISO Year
How to use Week Number Calculator
- 1Pick a date (defaults to today).
- 2The ISO week number and year update instantly.
Why use this tool
- Uses the ISO 8601 standard, where week 1 is the week containing the year's first Thursday.
Frequently asked questions
Why does the ISO week number sometimes differ from the calendar week?
ISO 8601 weeks always start on Monday and week 1 is defined as the week containing the year's first Thursday, which can differ from simpler 'week since Jan 1' counting methods.