The following are examples of acceptable reasons for missing an exam.

Medical reasons: Absence from an exam due to medical reasons can be planned or unexpected.  If planned, you need to notify your instructor at least two weeks in advance of the exam.  If unexpected, you will need to contact me within a day of the missed exam.  In either case, you will need to give your instructor: your full name, student ID number, your section number, email address, and documentation from a medical professional, with a telephone number where the professional can be contacted if necessary. You need not disclose any details of the reason for a medical excuse, but there must be enough information to allow the absence to be excused.

Religious observances: State law and University regulations require that a student be excused from academic pursuits on days of religious observance. The regulations also require the student to notify the instructor, in writing, at least two weeks before the absence or it may not be excused.  The University provides a list of major observances here