Nobody knows the exact formula apart from Jagex themselves. And some of the TipIt staff as they claim their combat clac to be 100% accurate... EDIT: Right now, runeweb's sig says I'm 103 combat, but I'm 102 combat and 1 prayer, def, atk ,etc, away from 103 combat. TipIt's calc on the other hand was right, I'm not yet 103 combat.