I'd store levels anyways, because each time tables change, you're going to have to determine what to store so you are writing the calculation code anyways in case it turns out storing wasn't a good idea, so you can fall back to deriving. either way you have to code the derivative value calculator. the reason I'd store tho, is that once someone levels up, I think it's be an odd expectation to be demoted somehow but then again depends on the game I guess. I get demoted back to moron often when I'm playing chess haha still they're not going to derive my rating each time so they store it.