Cars & Other Vehicles How much is insurance at the age of 18? How much is insurance at the age of 18? The average cost of full-coverage auto insurance for 18-year-olds is $7,396 per year, or $616 per month, according to our research. Erie offers the cheapest car insurance for 18-year-olds, with an average annual rate of $3,173.Dec 7, 2021