Car insurance is yet another cost that joins that seemingly endless list. Adding a teen to a family policy raises the premium by 50 to 100%, according to the Insurance Information Institute. In terms of a dollar amount, CarInsurance.com data puts the average cost of adding a teen at $3,594 per year, or about $299 per month. That baseline cost typically rises once a teen driver is added to the household, in some cases by several hundred dollars a year, so ask your agent for a quote that reflects your teen specifically. Even seemingly unrelated factors, like your teens' grades or whether they are going to school far away, can affect their car insurance.