As a rule of thumb, the more formal the event, the longer the lead time should be. For example, wedding invitations should be mailed six to eight weeks ahead of time, whereas for a bar or bat mitzvah, four to six weeks ahead is plenty. Earliness is also encouraged if there’s a high chance of conflicts, such as during the holiday season when guests are likely to be invited to multiple events. For less formal affairs, such as a very casual dinner party or get-together, a heads-up of a week or two should be sufficient.