Mathematics for physicists

I was thinking of double majoring with mathematics to complement my bachelor's in physics, but this would end up extending my graduation by a year (two semesters), cost more tuition over my financial aid, and make me double up/ add another class onto my normal fall/spring credits. Would I just be better off studying more mathematics on my own time during the summer to be better prepared for graduate school? If anything I'd love to study both in graduate school but I don't really think I can juggle both at this point of academia. Again, just for my bachelor's.

Are you doing theory or experiment?  Experimentalists don't require that much crazy math.

I don't think you should delay graduation by a yr...