When selecting items for one's paper trousseau, very few brides neglect to order reply cards and envelopes. These have become "essentials" when attempting to calculate the number of guests to expect at the reception.
However, having sent them out with the invitation package, know that there will always be a number of guests who never bother to reply. Your choice is to go with some industry average that calculates that up to 10% of invited guests won't attend and won't let you know they aren't coming so you can plan accordingly or you may wish to contact those "silent" guests directly and ask if they are planning to attend.
Some brides elect to make the calls themselves, others involve their mothers in the contacts or the groom's mother as well. As Martha Stewart says, "Once the R.S.V.P. deadline printed on the reply card is come and gone, you are well within bounds to start reaching out to tardy invitees."
When you do call, keep the message short and sweet. Martha suggests these words: "I wanted to be sure you got our wedding invitation. I need to get the final numbers to my caterer this week, and we'd love to know whether we'll be seeing you there."
We know that some brides-to-be are considering a "B-list" of invited guests. We don't condone that practice but know that it happens. Some advice: If you are planning to use this approach, we offer these considerations: Most people will figure out they are "second-tier" guests when the invitation comes to them two weeks before the wedding date. If you are determined to use a second round of invitations, at least be strategic about it and up the dates when your invitations go out. Send your first round of invitations out up to 10 weeks in advance and set the R.S.V.P. to at least 5 weeks before the wedding date. Once regrets start coming in, you can still get a few invitations out to names on the B-List if you are determined to do so.