This online Week Number Calculator finds the week number in year from the known date using the Gregorian calendar. It supports both ISO 8601 and USA/Canada week date systems. Enter the year, month and day, then choose the respective week numbering system and click the “Calculate” button to get the week number.
Week number in year
The ISO week numbering system (accepted in Europe) assumes that each year has 52 or 53 full weeks. Weeks start on Monday. The first week of the year always contains 4th of January and the first Thursday of the Gregorian year.
The US week numbering system (accepted also in many other English speaking countries) has weeks from Sunday through Saturday. The first week of the year contains 1st of January and the first Saturday of the Gregorian year. As a result this system has partial weeks at the beginning and the end of the year. For example, the first week of the year 2022 consists of only one day – Saturday, 1st of January!
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Check out our other date & time calculators such as Day of Week Calculator or Day Counter Calculator.