Week numbers in Microsoft Excel
To calculate the ISO 8601 week number in Microsoft Excel, use the following formula:
=ISOWEEKNUM(A1)
* Ensure your system or application regional settings are set to follow ISO 8601 standards (weeks start on Monday) if the output varies.
Step-by-Step Instructions
- Put your date in a cell, for example A1.
- In another cell type =ISOWEEKNUM(A1) and press Enter.
- The result is the ISO 8601 week number (1 to 53).
- For today's week number use =ISOWEEKNUM(TODAY()).
Good to Know
Do not confuse ISOWEEKNUM with the older WEEKNUM: plain =WEEKNUM(A1) uses the US convention (week 1 contains January 1, weeks start Sunday) and disagrees with the ISO number in most years. WEEKNUM(A1, 21) is equivalent to ISOWEEKNUM for backward compatibility.