Rating systems
Elo, Glicko and Glicko-2
Published Updated
All three systems try to predict results from previous results. The important difference is uncertainty. FIDE’s Elo implementation assigns a development coefficient called K; Glicko also keeps a rating deviation; Glicko-2 adds volatility, which models how variable a player’s underlying strength appears to be.
On this page
FIDE Elo in one game
FIDE looks up the expected score from the rating difference, subtracts that expectation from the actual score (1, ½ or 0), and multiplies the result by K. It sums those changes across the rating period and rounds the period total. The current regulations use a published probability table, not an unrounded logistic answer displayed to many decimal places.
What rating deviation changes
A Glicko rating comes with a measure of uncertainty. A new or long-inactive player has a wider estimate, so results can move the displayed rating quickly. An established player with a narrow deviation normally moves less. This is why two equally rated players can gain different amounts from similar-looking wins.
What Glicko-2 adds
Volatility estimates how much a player’s strength tends to fluctuate between rating periods. It is not a mood score and it does not make a rating directly comparable with another site. It is another input used to update the rating and its uncertainty.
Which organisations use which system?
- FIDE: its published Elo implementation and tables for standard chess, with separate rapid and blitz lists.
- Lichess: Glicko-2, documented by Lichess itself.
- Chess.com: a Glicko-based system, as described in its own help centre. Its pools and settings are its own, so do not substitute another site’s calculator.
What survives every system
Ratings are relative to the people producing results in that pool. Even identical code would not make two separate pools equivalent. Use ratings to arrange competitive games and measure a trend within one category; use game analysis to decide what to study.
Sources and scope
- FIDE Rating Regulations, article 8.
- Lichess: Chess rating systems.
- Chess.com: How do ratings work?
- Mark Glickman’s Glicko papers and explanations, the primary technical source for Glicko and Glicko-2.
Regulations and platform implementations can change. These notes were checked on 16 July 2026; follow the linked first-party source for the current wording.