Setting Page Break based on Number of Months in a matrix

Hi,

I have a matrix showing data group by month(Column group). I added this matrix inside a list control to have page break for each 12 rows. The report has Begin date and end date. There is a requirement like if the begin date starts with say Apr 2011 and end date as Aug 2014, then the first row group of list should show data from Apr 2011 to Dec 2011 and next row group should show from Janualry Month. i.e., Jan-12 to Dec-12(Second Row group), Jan13-Dec13), Third Row Group. Then Jan14 to Aug 14.

if the begin date starts with say Sep 2011 and end date as Aug 2014, then the first row group of list should show data from Sep 2011 to Dec 2011 and next row group should show from Janualry Month. i.e., Jan-12 to Dec-12(Second Row group), Jan13-Dec13), Third Row Group. Then Jan14 to Aug 14.

I tried with below approach to show variable number of rows per page.

Floor((RowNumber(nothing)+9)/12).

I need to tweak above expression some how to achive the actual requirement stated above. Can anyone help me to achive this requirement?