Authorized User/Credit Card/Credit Score

[Robert Fullum]

I'm listed as an authorized user on a few of my parents' credit cards. My plan is to buy my first investment property in about 18 months and i'm trying to get my credit score as high as possible during this time. 

Their credit history is excellent, but their cards do have a fair amount of debt held on them. Removing myself as an authorized user could either help my score (lower utilization ratio) or hurt my score (shorten my credit history, make the few dings on my credit more prevalent.) 

Is there a formula or a resource somewhere i can use to find out if de-authorizing me from those cards will help or hurt my score?