<prompt> Human: Basically my mom wants to add my sister as an authorized user on her credit card in hopes of helping my sister build credit. She asked me if that would work, but Ive got no clue! Possibly important notes- Sister would be added to a credit card of moms that is in good standing and approx 3 years old. Limit of 5k. Rarely used with no current balance.Moms credit in general isnt the best. Her score is in the 640s. Sisters credit is currently nearly non existent. Shes got one thing on it, and its a high interest vehicle loan-that she NEVER should have gotten :. I havent actually got a clue how the nuances of credit scores work. Mine is actually decent but I THINK only because Ive paid on time, paid off multiple financed vehicles and boughtsold homes over the years. or it might be from that one time when I blew out my candles and wished for a 730 score.  <response>: Yes, it will impact her credit score. So long as the account is in good standing and the use ratio is low, itll help. 3 years isnt very long, but time keeps moving along, so over time itll improve things. 