If you use week numbers in your workbooks then be aware that there are different
week number systems in use in the world.
If you order for example lingerie from Paris for your wife and want to have it in week 5 (2005)

Note: WEEKNUM is an Analysis ToolPak function

Excel WEEKNUM (first day Sunday): 23-jan-29-jan
Excel WEEKNUM (first day Monday): 24-jan-30-jan
ISO week number (first day Sunday): 31-jan-6-feb

You see that you have a big problem

On Chip Pearson’s site you can find all the information you need about week numbers.
http://www.cpearson.com/excel/weeknum.htm

But Norman Harker and I created a week calendar file that might be usuful.
http://www.rondebruin.nl/weeknumber.htm

It shows you all the dates and week numbers from a certain year on one printable page.
There is a separate sheet for the following week numbering systems :

1) ISO Week numbering: Week 1 starts on Monday of the week with the first
Thursday of the Calendar Year.

2) Excel WEEKNUM function (optional second argument of 1 (default)). Week 1
starts 1-Jan with subsequent weeks starting on a Sunday and final week ending on 31-Dec.

3) Excel WEEKNUM function (optional second argument of 2). Week 1 starts
1-Jan with subsequent weeks starting on a Monday and final week ending on 31-Dec.

4) Simple week number. Week 1 starts on the first day of the year.

I will release a new version of my EasyFilter add-in next week with a Date tab with
options to filter on week numbers, weekdays, months, years, quarters,….)

Ron de Bruin
http://www.rondebruin.nl/