Im turning 18, im gonna be added to my parents insurance, how much will it go up?

they have geico, and im a male, i know that 18 male looks bad, but i do have a 3.3 GPA. do tey take that into accout? i think they pay 120 a month now, how much a month will it be after im added? i also have had my permit for almost a year and no traffic tickets or violations at all!