Take a given school's average MCAT. Add 10 times the school's average gpa. Subtract 1. Call this the school's NUMBER.
If your (gpa)(10) + MCAT = NUMBER then you are an adequate candidate academically (your ECs can raise or lower your strength as an applicant). (if you did a post-bach to make up for a poor undergrad gpa use the post-bach gpa times 8 rather than your undergrad gpa times 10).
If your NUMBER is 1-2 points higher, then you are an average candidate. More than 2 points higher, you have a better than 50-50 chance of getting an interview (most schools only interview a small fraction of the applicant pool).
If your NUMBER is 1-5 points lower but you bring some special skills or experience to the table, then you may be suitable for admission and have a shot at getting an interview if the circumstances are right.
If your number is >=79 you've got nothing to worry about. If your number is <50, you do not have a prayer.