Credit Karma is accurate in the sense that it gives information about the data in a credit report and contains the latest information reported by creditors to the TransUnion credit bureau. Information is sometimes outdated when creditors have not recently updated a credit report. On the other hand, Credit Karma is not accurate in terms of FICO credit score, which is the "official" score most often used by creditors.
Scores that are not FICO scores are often called FAKO scores. The credit score given by Credit Karma is a FAKO score that is generated using Credit Karma's specific scoring algorithm. It is often times not comparable to FICO, but sometimes the two scores are close, mainly due to coincidence. The Vantage Score is another type of credit score that is sometimes used by creditors, and it is also different from Credit Karma's score. Additionally, creditors sometimes use a score generated by their own in-house algorithm, and there are even different types of FICO scores depending on the exact FICO algorithm being used. Since there are so many types of scores for creditors to choose from and because a credit score can change from day to day, no credit score algorithm is truly accurate.