Question : Is there a way to use the weeknum function wiih non statndard dates?

Is there a way to adjust the weeknum function to start at a specific Date?  I need to group transactions by week from Friday to Thursday, for each week of the year.    For example in 2009 week 1 would be 1/2/09 to 1/8/09, in 2008 it would be 12/28/07 to 1/3/09

Answer : Is there a way to use the weeknum function wiih non statndard dates?

Ok I still don't see why week 1 would start on 28th December (why wouldn't it start on 4th Jan?) but if you just want to sum transactions per week then you could use this method:

Assume dates are in A2:A1000 and transaction amounts in B2:B1000 then you could put the first week start date in D2, e.g. 12/28/07 and in D3 copied down

=D2+7

to give a list of all week start dates

Then in E2 copied down for a sum of transactions for that week

=SUMPRODUCT((A$2:A$1000>=D2)*(A$2:A$10007),B$2:B$1000)

regards, barry