There is a good article on estimating alimony in northern Va written by Jeff Krause

http://www.divorcesource.com/VA/ARTICLES/krause11.html

In this article he provides a formula.

My question ... is the resulting amount the estimated annual alimony payments (leaving the number of years this calculated amount must be paid to be determined by the court), or is it the a total amount (leaving the dispersal up to the court)?

Hope this makes sense.