Update:

I recently found on Pearson's website both a formula and VBA code for
calculating week numbers without the need for the Analysis Toolkit
add-in.

I tested the formula against the weeknum() function for all dates in
this current (2005) calendar year and it returned the same value for
each date.

First, credit where credit is due:
http://www.cpearson.com/excel/DateTimeWS.htm
http://www.cpearson.com/excel/weeknum.htm

See the first link for the formula he recommends and the second link
for a VBA module that will do the same thing.


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nbrcrunch