Ok after reading this thread from start to finish as well as others I'm still a bit fuzzy and confused - I'm stuck on if you add an AU on an Amex, with their SS#, will that AU be affected by the primary cardholder's credit utilization? I'm helping out my cousins and I'm not sure what is the best approach for building credit for their 18 year old son (who got denied by Amex and I started him off with a cap1 & Citi). Both parents have scores in the low 700's, one 34% credit utilization (PRG) and one 67% (plat) both with timely monthly payments. Which card would be the best to add him as an AU on? What I'm not understanding is whether the credit utilization is going to affect his credit score and how it will show up on his credit report in terms of the card's history affecting how long his credit history is going to be. I really appreciate any advice/explanations/suggestions! Thanks!