Which website provides the most accurate MMR?
There is no number-calculating method given officially by Riot Games, and none of the other MMR-speculating websites use our numbers. Every calculation is based on assumptions.
Each and every MMR-providing websites has a different inner-algorithm used to speculate the numbers; and does not share its methods with the other.
We try our best to express summoners' abilities with numbers by reflecting on their past ratings, and to do so by updating our algorithms more than twenty times per two months.