Microsoft Office Tutorials and References
In Depth Information
Using WEEKNUM or ISOWEEKNUM to Group Dates into Weeks
• return_types of 11 through 17 were added in Excel 2010. 11 returns
Monday as 1 and Sunday as 7 (the same as using 2). 12 returns Tues-
day as 1, 13 returns Wednesday as 1, and so on, up to 17 returning
Sunday as 1.
Figure 11.42 shows the results of WEEKDAY for all 10 return types.
Figure 11.42. Columns B, C, and D compare the
Columns B, C, and D compare the WEEKDAY
WEEKDAY function for the
function for the
three different return_type
return_type values shown in row 3.
values shown in row 3.
WEEKNUM oor ISOWEEKNUM
ISOWEEKNUM to Group Dates into Weeks
to Group Dates into Weeks
WEEKNUM offers new options in Excel 2013. One of the new options is also
promoted to a new function: ISOWEEKNUM.
For many versions, Excel did not calculate weeks to match the ANSI stand-
ard. The new return_typeof 21 or the ISOWEEKNUM function returns the week
number to match the ANSI standard. In this system, weeks always start on
Monday. The first week of the year must have four days that fall into this
year. Another way to say this is that the week containing the first Thursday
of the month is numbered as Week 1.
In the ANSI system, you might have Week 1 actually starting as early as
December 29 or as late as January 4. The last week of the year is numbered 52