The amount of math a doctor needs depends on his or her field of practice. Emergency and Internal Medicine doctors have to calculate the amount of drugs they need to give to a patient. A radiologist has to know geometry in order to report the size shape location and proximity of tumors or fractures they see on xrays.
Most medical schools require applicants to have at least a semester of calculus. Take as many math courses as possible in high school. In chronological order, most high schools and many colleges offer students courses in pre-algebra, algebra 1, algebra 2 and trigonometry or pre-calculus.