This will depend on how competitive of an applicant you are. If you are a very competitive applicant, who has a high GPA, MCAT, and significant extracurricular achievements, you may only need to apply to 15 schools (mainly top tier schools). Most medical students, however, will need to apply to 20-30 schools in order to improve their chances at matriculating. If you are right at the average GPA and MCAT of matriculants (3.7 and 511), then you should probably apply to 30 schools. The more competitive of an applicant you are, the less schools you need to apply to.