The ISO_WEEKNUM() function returns the week number of a given date according to the ISO calendar.
The week starts on Monday and week 1 is the week that contains the first Thursday of the year.
Function name:
ISO_WEEKNUM()
Syntax
ISO_WEEKNUM(date)ℹ Calling function parameters in TimeTonic:
- $field_name = field (link, linked table column, number, selection, formula, text...).
- "free text" = free text to be added between quotation marks.
- do not use quotation marks for numbers.
Parameters
| Parameter | Description |
|---|---|
date |
Date for which to calculate the ISO week number. |
Example
ISO_WEEKNUM(2026-1-1)Result: 1
January 1, 2026 falls in the 1st ISO week of the year 2026.
Notes
Weeks start on Monday.
Week 1 contains the first Thursday of the year.
Works with all available date column formats.
Return type
The function returns a number (ISO week number).
The output type format of the result can be configured in the output field options of the formula editor. For more details, see Output format options in the Formula column article.
Function comparison:
| Function | Week start | Definition of week 1 |
|---|---|---|
| WEEKNUM(date) | Sunday | Week containing January 1st |
| ISO_WEEKNUM(date) | Monday | Week containing the first Thursday of the year |
The choice between WEEKNUM() and ISO_WEEKNUM() depends on the business context (internal planning, ISO standards, rounds, reporting)