Money How much gas tax adds to cost of filling up your car in every state February 5, 2019February 5, 2019Samuel Stebbins, 24/7 Wall StreetComments Off on How much gas tax adds to cost of filling up your car in every state The government levies an 18.4 cent tax on every gallon of gasoline. On top of that, each state imposes its own tax, which if often even higher.