The WEEKNUM function is used to return the number of a week for a given date in that particular year. Usually, a year consists of 54 weeks. Thus, this Function will return a number between 1 and 54. This function is an inbuilt function in Microsoft Excel and is categorized as a Date/Time Function. As a worksheet function, you can enter the WEEKNUM function as part of a formula in a cell. Syntax for the WEEKNUM functionRemember, this Function has two arguments, the first one is required and the second one is optional. serial_num:- (Required). A valid Excel date in serial number format. return_type:- [Optional] The day the week begins. By default, it is 1. I have created the infographics for WEEKNUM Function. With the help of these infographics, you can easily learn step by step process for using this excel functions. Furthermore, Excel consists of many inbuilt functions which are helpful in the analytical and statistical study of number. Simply follow the instructions in the infographics below:You can apply this function in excel using two different systems. System 1:− The week which reflects January 1st of that particular years is considered the 1st week of the year. Traditionally, the week starts on Sunday and is used by this system. System 2:− The week which reflects the first Thursday of the year is the first week of the year. It is the methodology specified in ISO 8601. It is commonly known as the European week numbering system. Generally, System 1 is widely used. Applicability: Excel 2007, Excel 2010, Excel 2013, Excel 2016 We thank our readers for liking, sharing and following us on different social media platforms. If you have any queries please share in the comment section below. I will be more than happy to assist you.