Doctors do not necessarily need calculus, probability, etc. in doing their job but the core skills in doing mathematics is transferrable (critical thinking/analysis, arithmetic skills, connection of different ideas). However, knowing the extra miles in mathematics is interesting in certain subjects of medicine, including pharmacology.
For example, we know that an antibiotic generally kills a bacteria by affecting the conditions in which it functions. However, the issue comes in the amount that should be consumed. By measuring the conditions in which the bacteria thrives at different levels of a condition (e.g. pH), we could use calculus to calculate the most efficient and effective point, thus the best solution to the antibiotics question. You can find out more by searching "calculus in medicine" and navigating to the sites.northwestern.edu website.