Why does the Elo I gain from games fluctuate so heavily?

Question

When I am playing on Chess.com, the amount of elo I gain or lose from each game seems to be randomized, due to the fact that I gain less and lose more elo, when playing against players with a higher elo rating than me. But when I am playing against players with a lower elo rating than me, I seem to generally gain more and lose less elo.

Answer 1

If the website was using ELO, then that would indeed be unusual. ELO is designed to change a lot after unexepcted results (beating someone much higher rated / losing against someone much lower rated) but very little after expected results.

But Chess.com does not use ELO. They are using the Glicko rating system. The difference between Glicko and ELO is that Glicko tries to take into account that ratings of players might have different grades of reliability. Ratings of new players in a community are notoriously unreliable due to lack of data. Players who don't play very often are also unreliable, because you don't know how much they practiced or slacked between matches. But there are also established and active players that can have widely varying performance depending on how they feel that day.

In order to account for all of these reliability problems of ratings, the Glicko system calculates a "Reliability Deviation" (RD) for each player. This is a number that represents how unreliable their rating is. When your RD is high, then you gain or lose more points after each game (so it doesn't take too long to get closer to your actual rating). When your opponent's deviation is high, you gain or lose fewer points (because playing against someone whose rating is unreliable isn't a good way to determine your own rating).

So if your goal is to change your rating quickly, try to play against players who are active and whose rating appears relatively consistent.