Rick,

I think perhaps we need more information, such as "What are your
criteria for 'counting weeks'?" That's kind of vague. In the
meantime, checkout DATEDIF:

=DateDif( StartDate, EndDate, "D") will give you a difference in
"days" between the entry dates.

(See Excel help for other argument types, including "Y", "M", "MD, "YM"
and "YD")

I don't think that fully answers your question, but it may get you
started until you can re-formulate the question to us.

Chris