This is how I chance.

Let us set up a potential applicant.
3.7 GPA
1900 SAT - 600 700 600
Decent EC's
Basketball Team 4 years
Chess Club President 4 years
MUN member 3 years
Debate Team 3 years
Statistics Club 2 years
Volunteer 50 hours
He/She is applying to University of Illinois--Urbana-Champaign Champaign, IL

SAT Critical Reading: 530 / 660 He is in the middle of this range
SAT Math: 680 / 770 He is in the lower half of this range.
SAT Writing: 570 / 670 He is in the middle of this range.
Average SAT 3.7 He is right around average.

From this data, it is PHYSICALLY SUPPORTED by DATE rather than opinion... that this person has a good chance to get in, and this school is a match for him.

This is a detailed example of what quality chances you will get on this website.

Student A Stats: 3.1 GPA UW 3.1 GPA W
1800 SAT - 600 600 600
Members of a lot of clubs, president of X club, also President of Y club.
26 ACT
Student A wants to go down to Pittsburgh, specifically UPitt.
SAT Critical Reading: 570 / 680 Lower Range
SAT Math: 590 / 680 Lower Range
SAT Writing: 560 / 660 Mid Range

Average GPA: 3.4 Lower than average
Based on the evidence, the SAT is right around the 25th percentile. His GPA is slightly lower than the average. His EC's are average/below average.

High Match