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ISOWEEKNUM
ISOWEEKNUM follows the ISO 8601 standard: week 1 is the week containing the year's first Thursday, and all weeks run Monday–Sunday. Use it for international reporting, manufacturing schedules, or any context where ISO week numbering is required.
Excel
=ISOWEEKNUM(DATE(2024,1,1))Google Sheets
=ISOWEEKNUM(DATE(2024,1,1))✓
Verified example
Computed by a real spreadsheet engine on the sample data below.
| ProjectDate | ISOWeek |
| 2024-01-01 | |
| 2024-01-08 | |
| 2024-12-30 | |
| 2024-12-31 |
=ISOWEEKNUM(DATE(2024,1,1))→1
Try it with your data
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How it works
- 1Store your dates as proper date values in column A.
- 2In cell B2 type =ISOWEEKNUM(A2) to get the ISO week number.
- 3Compare with WEEKNUM if you need to understand the difference between US and ISO week numbering for your dates.