The WEEKNUM Function in Excel will return the week number for a given input date. WEEKNUM Function: A Brief The WEEKNUM function in Excel is used to return the week number from a given input date. If the input is not a valid Excel date, the function will return a #VALUE! error. It will also return a #NUM! error if the return_type argument is not supported. The return_type must be 1, 2, or between 11 and 17. WEEKNUM week number input date not a valid Excel date #VALUE! error #VALUE! error #NUM! error return_type return_type 1, 2, or between 11 and 17 Objective

Value Returned by the function



Aim to return the week number

The WEEKNUM function in Excel will return the relative week number to the given input date. Objective

Value Returned by the function



Aim to return the week number

The WEEKNUM function in Excel will return the relative week number to the given input date. Objective

Value Returned by the function Objective Objective Value Returned by the function Value Returned by the function Aim to return the week number

The WEEKNUM function in Excel will return the relative week number to the given input date. Aim to return the week number Aim to return the week number The WEEKNUM function in Excel will return the relative week number to the given input date. The WEEKNUM function in Excel will return the relative week number to the given input date. WEEKNUM Function: A Syntax =WEEKNUM(serial_number, [return_type]) =WEEKNUM(serial_number, [return_type]) serial_number: The date you want to find the week number for. serial_number: The date you want to find the week number for. serial_number return_type: A number that determines which day the week starts on. This is an optional one. By default, Excel assumes Sunday as value 1. return_type: A number that determines which day the week starts on. This is an optional one. By default, Excel assumes Sunday as value 1. return_type The following is differences between the WEEKNUM and ISOWEEKNUM functions is, WEEKNUM Function

ISOWEEKNUM Function



Can start on Sunday (default) or Monday (based on return type)

Always starts on Monday



Week 1 is the week containing January 1st

Week 1 is the first week with at least 4 days (ISO 8601 rule)



Varies depending on chosen return type (1 or 2)

Follows the international ISO 8601 standard consistently WEEKNUM Function

ISOWEEKNUM Function



Can start on Sunday (default) or Monday (based on return type)

Always starts on Monday



Week 1 is the week containing January 1st

Week 1 is the first week with at least 4 days (ISO 8601 rule)



Varies depending on chosen return type (1 or 2)

Follows the international ISO 8601 standard consistently WEEKNUM Function

ISOWEEKNUM Function WEEKNUM Function WEEKNUM Function WEEKNUM Function ISOWEEKNUM Function ISOWEEKNUM Function ISOWEEKNUM Function Can start on Sunday (default) or Monday (based on return type)

Always starts on Monday Can start on Sunday (default) or Monday (based on return type) Can start on Sunday (default) or Monday (based on return type) Always starts on Monday Always starts on Monday Week 1 is the week containing January 1st

Week 1 is the first week with at least 4 days (ISO 8601 rule) Week 1 is the week containing January 1st Week 1 is the week containing January 1st Week 1 is the first week with at least 4 days (ISO 8601 rule) Week 1 is the first week with at least 4 days (ISO 8601 rule) Varies depending on chosen return type (1 or 2)

Follows the international ISO 8601 standard consistently Varies depending on chosen return type (1 or 2) Varies depending on chosen return type (1 or 2) Follows the international ISO 8601 standard consistently Follows the international ISO 8601 standard consistently Basic Example of Using WEEKNUM Function: The example covers the variable scenarios of using the WEEKNUM function in practical days. In the above example, the first five input dates are valid Excel dates, so the WEEKNUM function returns the correct results. valid Excel dates WEEKNUM However, the date 15-13-2025 is not a valid date, so the WEEKNUM function returns a #VALUE! error. 15-13-2025 not a valid date WEEKNUM For the next input, the formula used is =WEEKNUM(B10, 99). Since 99 is not a valid return_type number, the function is supposed to return a #NUM! error. Otherwise, Excel may ignore the invalid return_type and treat it as 1, and then return a normal result. =WEEKNUM(B10, 99) 99 not a valid return_type number #NUM! ignore the invalid return_type 1 A year has about 52 or 53 weeks, depending on leap years. The table below contains the WEEKNUM value for the corresponding week range. If the year is a leap year, then, This WEEKNUM function returns different return types for WEEKNUM(), and each one decides which day the week starts. Refer to the table below: return types Using the WEEKNUM Function With Other Nested Functions: Example Explanation: In the first example, the WEEKNUM function is used with the date April 10, 2025 (10-Apr-2025) in cell B4. It calculates the week number assuming Sunday as the first day of the week and returns 15.
In the second example, the formula calculates the week number assuming Monday as the first day of the week. It also returns 15 for the same date.
In the third example, the formula checks if the week number is even or odd. Since 15 is an odd number, it returns “Odd”.
In the fourth example, the formula dynamically calculates the current week’s number based on today’s date. The result will automatically update each day.
In the fifth example, the formula subtracts the current week number from 52 to find out how many weeks are left in the year. For April 10, 2025, it returns 37 weeks remaining.
In the sixth example, the formula checks whether the week falls in Quarter 2. Since week 15 falls between week 14 and 26, it returns “Q2”.
In the seventh example, the formula adds about one-fourth of a week’s span to the current date, resulting in May 6, 2025 (06-May-2025).
In the eighth example, the formula extracts the month number from the date. Since April is the fourth month, it returns 4.
In the ninth example, the formula classifies the date into either the First Half or the Second Half of the year based on its week number. April 10, 2025, falls in the First Half.
In the tenth example, the formula combines the year and the week number into a custom format like 2025-W15. In the first example, the WEEKNUM function is used with the date April 10, 2025 (10-Apr-2025) in cell B4. It calculates the week number assuming Sunday as the first day of the week and returns 15. first example WEEKNUM April 10, 2025 (10-Apr-2025) B4 Sunday 15 In the second example, the formula calculates the week number assuming Monday as the first day of the week. It also returns 15 for the same date. second example Monday 15 In the third example, the formula checks if the week number is even or odd. Since 15 is an odd number, it returns “Odd”. third example even or odd 15 “Odd” In the fourth example, the formula dynamically calculates the current week’s number based on today’s date. The result will automatically update each day. fourth example current week’s number today’s date update each day In the fifth example, the formula subtracts the current week number from 52 to find out how many weeks are left in the year. For April 10, 2025, it returns 37 weeks remaining. fifth example current week number 52 how many weeks are left April 10, 2025 37 weeks remaining In the sixth example, the formula checks whether the week falls in Quarter 2. Since week 15 falls between week 14 and 26, it returns “Q2”. sixth example Quarter 2 week 15 week 14 and 26 “Q2” In the seventh example, the formula adds about one-fourth of a week’s span to the current date, resulting in May 6, 2025 (06-May-2025). seventh example one-fourth of a week’s span May 6, 2025 (06-May-2025) In the eighth example, the formula extracts the month number from the date. Since April is the fourth month, it returns 4. eighth example month number fourth month 4 In the ninth example, the formula classifies the date into either the First Half or the Second Half of the year based on its week number. April 10, 2025, falls in the First Half. ninth example First Half Second Half April 10, 2025, First Half In the tenth example, the formula combines the year and the week number into a custom format like 2025-W15. tenth example year week number 2025-W15 Functions Used in the Examples: That’s it. This tutorial was originally published on How to Use Excel WEEKNUM Function? How to Use Excel WEEKNUM Function

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