Week Number Calculator — What Week of the Year Is It?
The Week Number Calculator tells you the ISO week number for any date. ISO weeks run Monday to Sunday; week 1 is the week containing the first Thursday of the year. Week numbers are used in manufacturing, logistics, project planning, and international business — particularly in Europe where week numbers appear on calendars and in contracts.
Frequently Asked Questions
A year has 53 ISO weeks when January 1 falls on a Thursday, or December 31 falls on a Thursday. This occurs roughly every 5–6 years. The extra week is week 53.