Calculating an ISO-8601 based WEEKNUM
From [Wayback/Archive] ISOWEEKNUM Function – How to Get the Week Number in Excel:
- If we are using an older version of MS Excel, we can use the function
WEEKNUM
. By default, the WEEKNUM
function uses an arrangement where Week 1
begins on January 1
, and Week 2
begins on the next Sunday
(when the return_type
argument is omitted, or supplied as 1
).
However, with MS Excel 2010 for Windows and MS Excel 2011 for Mac, we can generate an ISO week number using 21
as the return_type
: =WEEKNUM(date,21)
.
- There is no built-in worksheet function for ISO weeks before MS Excel 2010.
I tested that ISO-8601 week number calculation in with Excel 2011 on MacOS and Excel 2010 on Windows: the workaround works well for the dates mentioned in ISO week date – Wikipedia.
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