How to Use the ISOWEEKNUM Function in Excel

Below is a comprehensive guide on utilizing the ISOWEEKNUM function within Microsoft Excel and Google Sheets.

Introduction to the ISOWEEKNUM Function

The ISOWEEKNUM function determines the ISO week number of the year for any given date. According to the ISO system, week numbers range from 1 to 53. The first week of the year (Week 1) is defined as the week containing the first Thursday of that year.

Syntax

The syntax for using the ISOWEEKNUM function is consistent across both Microsoft Excel and Google Sheets:

ISOWEEKNUM(date)

Here, date refers to the date you wish to evaluate for its ISO week number.

Examples

Example 1: Basic Usage

Suppose cell A1 has the date “2022-09-15”. To determine the ISO week number for this date, you would use the following formula:

Date	Formula	ISOWEEKNUM Result
2022-09-15	=ISOWEEKNUM(A1)	37

Example 2: Applying ISOWEEKNUM in Google Sheets

The application in Google Sheets mirrors that of Excel. For a date entered in cell A1, the formula to find its ISO week number is:

=ISOWEEKNUM(A1)

Use Cases

Tracking project timelines by referencing ISO week numbers.
Organizing work schedules or events utilizing ISO week number categorization.
Deriving week-based metrics or Key Performance Indicators (KPIs) for comprehensive business analysis.

Employing the ISOWEEKNUM function allows for seamless integration of ISO week numbers into your date-centric calculations and analyses in both Excel and Google Sheets.

More information: https://support.microsoft.com/en-us/office/isoweeknum-function-1c2d0afe-d25b-4ab1-8894-8d0520e90e0e

Other functions

DATE

Returns the serial number of a particular date

DATEDIF

Calculates the number of days, months, or years between two dates This function is useful in formulas where you need to calculate an age

DATEVALUE

Converts a date in the form of text to a serial number

DAY

Converts a serial number to a day of the month

DAYS

Returns the number of days between two dates

DAYS360

Calculates the number of days between two dates based on a 360-day year

EDATE

Returns the serial number of the date that is the indicated number of months before or after the start date

EOMONTH

Returns the serial number of the last day of the month before or after a specified number of months

HOUR

Converts a serial number to an hour

MINUTE

Converts a serial number to a minute

MONTH

Converts a serial number to a month

NETWORKDAYS

Returns the number of whole workdays between two dates

NETWORKDAYS.INTL

Returns the number of whole workdays between two dates using parameters to indicate which and how many days are weekend days

NOW

Returns the serial number of the current date and time

SECOND

Converts a serial number to a second

TIME

Returns the serial number of a particular time

TIMEVALUE

Converts a time in the form of text to a serial number

TODAY

Returns the serial number of today's date

WEEKDAY

Converts a serial number to a day of the week

WEEKNUM

Converts a serial number to a number representing where the week falls numerically with a year

WORKDAY

Returns the serial number of the date before or after a specified number of workdays

WORKDAY.INTL

Returns the serial number of the date before or after a specified number of workdays using parameters to indicate which and how many days are weekend days

YEAR

Converts a serial number to a year

YEARFRAC

Returns the year fraction representing the number of whole days between start_date and end_date