Calculate the new Elo ratings for two players after a game, based on who won and the K-factor used.
Elo is a rating system originally designed for chess, now used across many competitive games, that estimates relative skill and updates after every match based on the result and how surprising it was.
Expected Score (A) = 1 ÷ (1 + 10^((Rating B - Rating A) ÷ 400))
New Rating = Old Rating + K × (Actual Score - Expected Score)
A 1500-rated player beating a 1450-rated player with K=32 gains a modest number of points, since they were already the favorite to win.
It's a method for calculating relative skill levels in competitive games, where ratings go up or down based on match results, weighted by the opponent's rating.
New rating = old rating + K × (actual result − expected result), where the expected result is based on the rating difference between players and K is a sensitivity constant.
Elo's expected-outcome formula predicts a lower-rated player is less likely to win, so an upset win yields a bigger rating adjustment than an expected win.