I hate sounding like a broken record, but here we go again.
The cost of a first-class stamp is going up to 44 cents on May 11. You can avoid shelling out the extra pennies if you stock up on Forever stamps, of course, but most of my clients aren't crazy about adorning their pretty invitations with the Liberty Bell.
I always recommend that clients take a complete invitation set to the post office for weighing. They'll tell you exactly how much postage is required and you'll have peace of mind that your lovely invites will get to their recipients safe and sound. WARNING WARNING WARNING: If your response deadline falls AFTER May 11, be sure that the stamps you affix for your response cards account for the rate increase: additional two cents for a 1-ounce envelope or one cent for a standard postcard.
I know it's a pain. Believe me, I know.