When planning a wedding, it is customary to send out invites at least twelve weeks in advance of the ceremony. This gives the guests sufficient time to clear their schedules, organise their travel, and respond to the invitation.
However, if you are expecting a significant number of guests from out of town or if you are organising a wedding in a remote location, it is a good idea to send the invitations out even further in advance, at least 5 months in advance. This will ensure that your guests are able to attend your wedding by providing them with sufficient time to make any travel preparations that may be required. It is also a good idea to send a save-the-date card or email to your guests several months in advance.
This is especially important to do if you are planning a wedding during a peak travel season or if you have a significant number of guests who will be travelling in from out of town. Your visitors will appreciate having this head's up, since it will allow them to better organise their schedules.