We get asked this question a lot! The vague answer is that you should send out invites far enough for guests to plan but close enough so that they do not forget about the party. Generally speaking, this is about 4-6 weeks in advance. This rule works well for most birthdays, showers and dinner parties. Casual gatherings require very little notice, so 2-3 weeks in advance is plenty. However, if travel is required for certain guests to attend the party, then 2-3 months in advance is necessary to allow for booking travel at reasonable costs.
Happy planning! As always, we are here to help!