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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.

ProjectDateISOWeek
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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Sample data — click any cell to edit

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How it works

  1. 1Store your dates as proper date values in column A.
  2. 2In cell B2 type =ISOWEEKNUM(A2) to get the ISO week number.
  3. 3Compare with WEEKNUM if you need to understand the difference between US and ISO week numbering for your dates.

Need a version for your data?

Try: “Get ISO week numbers for my European project timeline”

Related

TODAY / DATEDIFEOMONTHNETWORKDAYS

Written and reviewed by FormulaCraft Team. Each formula on this page is run through our verification engine before publishing.

Last reviewed: