<prompt> Human: So Im checking on the Discover App I have a Discover card, and it says there my FICO score is X. I jump into credit karma, which shows TransUnion and Equifax, and theyre both X - 42. Experian app wont show me my score with them unless I pay them. I know different agencies report different things at different times, but could I get an ELI5 on why different sources are off by that much? I can understand a few points but 42 points off seems excessive  <response>: Discover uses FICO Credit 8, and CreditKarma uses VantageScore.Vantage is not FICO, no matter how hard it tries to be. FICO scores, of which there are many, are all trade secrets and no one knows the exact formula. VantageScore tried to estimate it and sometimes does an OK job.For what it was worth, I applied for a new credit card recently. Discover said 789, CK said 738 and 739, and Chase who pulled the card said 740. So, in my case, CK won. 