Not really, when you sign on as a co-borrower, you are equally responsible for the debt so it will hit your CR. Your scores were in the 8s, how are they now? A 30 day is nowhere near as devastatign as a ninety day in about six months you probably shouldn't see a real difference in your scores. Time will cure all so if you're still mid 7s you shouldn't have a problem and most lenders will overlook the cosigned loan as they realize you may not have been aware that they went past due for such a short period of time.