I want to calculate total weeks between two dates.
Complexity is that we have a defined number of weeks in a month as follows
July Aug Sep Oct Nov dec Jan Feb Mar Apr May Jun
4 4 5 4 4 5 4 4 5 4 4 5

E.g.s
Start date End Date Req. Answer (Cum Weeks)
Jan'09 Mar'09 13
Dec'09 Mar'10 18
Aug'09 Sep'10 61 (One full year + 9 weeks for Aug'10 and
Sep'10)