Guess Who is Coming to the Wedding?

At this point..I really do not not know. I have a preliminary guest list that I need to review. Since time seems to be speeding up towards my wedding day and so many other things need to be finalized, but they are all based off of one thing..the guest list. I know that I can not invite everyone that I know, but how do you determine who stays and who goes?My mom has broken down the list to church folks, friends and family. I know that everyone who is invited will not show up or I will have persons who RSVP and do not show up, but I have to be prepared if they do. Which means I need seating for guest, tables for reception, linens, favors, and on and on and on. Whatever I do I have to have it figured out before the end of the month so that other deposits and plans can be made. How are you going to finalize your guest list?