It depends on the number of guests that will be traveling and how far. Generally speaking, the more people traveling, the longer the advance notice. Mail your save-the-dates 4 to 6 months in advance for local events and when a minimal number of people are coming in from out of town. Send save-the-dates 9 to 12 months in advance if more than half or all of the guests are traveling, like to a destination wedding. Don’t forget to send the invitations, too! Those should be sent 3 to 6 months before the event date, and well after your save-the-date postcards.