# ISOWEEKNUM

Formulas / ISOWEEKNUM
Calculate the ISO week number for a date.
`ISOWEEKNUM(date)`
• date - required date-time code for dates and time calculations

## Examples

• `=ISOWEEKNUM(A2)`

The ISOWEEKNUM function is used to return the ISO week number for a given date. For example, the formula returns 10 for the week of 3/9/2012 because that week begins on Monday (10).

• `=ISOWEEKNUM(TODAY())`

The ISOWEEKNUM function can also be used to return the week number of the current date. For example, the formula will return the current week number.

• `=ISOWEEKNUM(DATE(2017,1,1))`

The ISOWEEKNUM function can also be used to return the week number of a specific date. For example, the formula will return the week number of January 1, 2017.

• `=ISOWEEKNUM(A2)`

The ISOWEEKNUM function can also be used to return the week number of a date stored in a cell. For example, if cell A2 contains the date 3/9/2012, the formula will return 10, the week number of 3/9/2012.

## Summary

The ISOWEEKNUM function is used to determine the ISO week number of a given date. It can be used to quickly and accurately identify the week of the year for a specific date.

• The ISOWEEKNUM function takes a date argument which must be in serial number format.
• The week number returned is based on ISO standards.
• The ISOWEEKNUM function starts the first week of the year on the first day and increments on Sundays.
• The week is also started on the first week that contains a Thursday.