Did you send a Save the Date Card?
If you already mailed or emailed a save the date to your guests, you may have a little leeway on your invitation mail date. By alerting them early, many of your guests may have your event date already on their calendar. Likewise, if you've notified your out of town guests, they may have already booked their travel. But, this should not be a given, as many guests before receiving an invitation comes with some risks.
The best date to send your invitations
The general rule is to mail your invitations 8 weeks before your event. If some of your guests are traveling a long distance, you may even wish to add a few extras days as mail can be delayed. Guests located out of the country should either receive their invitations earlier, or if this isn't possible, alert them so they may plan their travel well in advance of your date. If you are having a destination wedding where guests will be traveling to your event location, you may wish to mail invitations about 10-12 weeks before your event.
Ideally, your guests will receive their invitations a full month before they need to RSVP and you will have all RSVPs in hand 3 weeks before your event. This also allows you some time to track down guests who have not responded. Of course, you'll want to check with your venue planner to verify when they need your final guest count.
Mailing save the date cards
If you are sending save the date cards, mail or email those 4-6 months in advance of your event date.