18th Birthday Invite, A person just can't leave your door open. This means, don't forget to put a precise date for the invited guests to react by. Try to be specific. Consider locating a specific date for the guests to respond by. A good example of such date commitment invite is "Please RSVP by Friday, 04 8th". Going one step further can sound right too. You can say: "Please respond no later than Friday, April 8th. Give thanks to you".
Try and be specific. 18th Birthday Invite, In other words, insist that even if people will not be attending, they contact you with a "negative" response. A new good way to do this could be to put in a note that claims "Please, do respond with a "Yes" or "No" to help us plan. "