calculators
Week Number Calculator
Find the ISO week number and year for any date. Shows the day of the week and explains the ISO week system. Free and client-side.
Frequently Asked Questions
What is an ISO week?
ISO weeks start on Monday. The first week of the year is the week containing the first Thursday.
Can the week number differ from the calendar year?
Yes. Some dates at the start or end of a year may belong to a different ISO year than the calendar year.
Is my data sent to servers?
No. All calculations happen locally in your browser.