How much does legacy help chances?

Hey guys, my mother got her masters from CMU (in the course of a year), she doesn’t donate though. By what margin would this help my chances?

Here are my other stats:

Major: Computer Science
GPA (4.0): 3.95
GPA (my school’s system): 5.52
Class rank: 42 out of 800 (almost top 5%), pretty competitive high school
ACT: 35 (sending)
SAT: 1530 (didn’t send)
Subject Tests:
Math II: 770 (Going to retake!!! I swear to God I will get an 800!)
Physics: 710 (Same story here! I didn’t know any Physics II when taking it and I have studied much more since. Most likely 800 soon)
Texas resident
Courseload: AP Human Geography freshman, AP World History sophomore, AP Calculus AB, Computer Science, English Language, U.S. History, Physics I junior, AP Calculus BC, Statistics, English Literature, Macroeconomics, Physics II senior, everything else GT/pre-AP.
Race: Asian
AP scores (if that matters): 5s on Human Geography, Calculus AB, Computer Science, English Language, Physics I, U.S. History.
Awards/Honors: Eagle Scout, AP Scholar, National Merit Commended, A Honor Roll

Extracurriculars:
Boston Crusaders Drum and Bugle Corps, tuba player, toured US throughout the summer and placed 6th in DCI World Championships. 84 hrs/wk, 12 wks/yr.
Boy Scouts of America, troop guide, quartermaster, cook, 2 hrs/wk, 46 wk/year.
High School Band, tuba section leader, BOA and UIL state finalists, 16 hr/wk, 40 wk/yr
National Honor Society, member, 1 hr/wk, 40 wk/yr.

My biggest worry is class rank and lack of STEM extracurriculars. This is definitely my reach school, but why not try
¯_(ツ)_/¯

Bump, but just for the original question.
My whole family went to CMU and I wonder about this as well.

In the CMU common data set https://www.cmu.edu/ira/CDS/pdf/cds_2017-18/c-first-time-first-year-admission.pdf legacy (listed as alumni/ae relation) is listed as IMPORTANT so it definitely means something. If you’re borderline, it might pull you up.

as a Legacy (ME degree in the 80;s) I ask this about my S19 who will want to apply. I have not been donating money over the years, and I am staring at the donate card, wondering if I should do so, but if I do, will it hurt him, as it will look like I am donating now to help get him in, but then again ,they will get some money and might see me as donating more if my son was to get in?

Several years ago I attended a CMU alumni event and since my son was just starting his college search I asked this question to director of alumni relations who also was in attendance. He said that legacy status was used as a tie-breaker amongst otherwise equally-qualified candidates. So simply being a legacy won’t get you in unless you’ve got the goods.