Calculus is not necessary to gain admission to medical school; very few medical schools--prestigious med schools--require calculus for admission. Even so, you can still earn an admission offer from one of these schools without any calculus under your undergrad belt. The requirements for med schools must be completed prior to MATRICULATION (i.e., 1st day of classes), not admission.
In spite of the fact that most med schools do not require it, I still recommend that you take calculus. It's an interesting subject, and it's not that difficult. In fact, calculus per se is easy--it's the algebra that kills people! Calculus will provide you with yet another perspective on phenomena, and broadening your perspective is key in college.