Week Number Calculator
Find the ISO week number for any date, along with a full-year week calendar.
Select a date to see its week number
Documentation
How It Works
This calculator uses the ISO 8601 standard. Weeks start on Monday, and Week 1 is the week containing the year's first Thursday. The ISO week year may differ from the calendar year at the start/end of the year.
The year calendar shows all weeks for the ISO year of the selected date. Click any week row to jump to that week's Monday.
ISO 8601 Rule
- • Weeks start on Monday
- • Week 1 has the year's first Thursday
- • 52 or 53 weeks per year
- • Jan 1–3 may be in week 52/53 of prior year
Disclaimer: For informational purposes only.
Frequently Asked Questions
Sponsored