How many grades or credits lower than A can a pre-med afford?
The answer can be determined with simple math.
For example, suppose the target GPA is 3.7 to avoid automated screenout or downgrading of one’s medical school application due to GPA being too low (of course, MCAT must also be high enough, but that is not the subject of this post). If we assume 120 credits of graded course work during undergraduate, 3.7 * 120 = 444, which is 36 less than 4.0 * 120 = 480. (Actual amount of graded course work may vary, since some students may have graded college course work taken while in high school, during summer sessions, or by overloading, while others use AP or similar credit to take fewer credits of graded course work.)
So this pre-med has 36 grade points of “slack”, and wants to avoid using it up. Each grade lower than A uses up some of the slack, in proportion to the grade and credits. For example, an A- (3.7) in a 5 credit course uses up (4.0 - 3.7) * 5 = 1.5 grade points of slack, while a B+ (3.3) in a 3 credit course uses up (4.0 - 3.3) * 3 = 2.1 grade points of slack.
Obviously, the calculation is different for different credit systems and different grade scales (but remember to convert grades to the AAMC values, which may differ from those used by some colleges). For example, if the college uses one credit per course, with 32 courses normally completed for a bachelor’s degree, and the college’s grading scale has A, AB, B, BC, C as the passing grades, then the pre-med has 9.6 grade points of slack, and an AB grade a standard course uses up (4.0 - 3.5) * 1 = 0.5 grade points of slack.
In addition, a parallel calculation should also be done for biology, chemistry, physics, and math (BCPM) courses, though the total number of credits of graded BCPM course work can be flexed more easily than the total number of credits of all course work (e.g. by whether to choose a BCPM elective versus a non-BCPM elective).