It’s been over 2 years since Wulfenia’s thread and 3 years since mlopezviedma’s article on OGS Ratings and Ranks. As we still get questions on the chat about ratings/ranks, I thought this may be a good timing to help newcomers by revisiting and clarifying OGS rating system.

OGS rating system is quite similar to EGF rating system in its use of Elo except in the handling of 9x9 and 13x13 games. While OGS accommodates other odd sizes, ‘ranked’ status can be given to 19x19, 13x13 and 9x9 games only, where 13x13 game result is weighted 1/2, and 9x9 results are weighted 1/4 of 19x19 for the calculation of rating points given/taken.

There is no difference in the amount of rating points given to a win by 100.5 points, by 0.5 points, by resignation, by moderator decision, or by timeout.

Calculation of rating points given is done once only at the end of a game, including the determination of player rating/rank. As player rating can change during a game (especially in long correspondence games), we cannot determine the expected rating point gain/loss at the time we accept a challenge. This makes the calculation to be accurate only at the end of a game. It is not uncommon a player rank jumps up or down significantly by moderator decision, especially on new players.

Overall rating/rank is not the average of other ranks. Instead, Overall is calculated with opponent’s Overall rating on all ranked games we play regardless of time setting.
When we win 1 Blitz, 1 Live and 1 Correspondence games, Overall gains 3 games worth of Elo points, while individual timeclass based ratings get 1 game worth each. 
When we are moving up in the ranks, we are winning more games than we lose on the average, and this condition causes Overall to move up quicker than other individual ratings on the average. If we are moving down in ranks, Overall moves down quicker. As the majority of players are getting stronger as time goes by (right?), Overall rating of our opponents (on the average) tends to be higher than other ratings, which further accelerates the Overall to move up quicker than others.

As explained in the above #3, OGS rating calculation is not done periodically. So, how well our opponents do after the game has no effect on our ratings, and our own inactive period also has no effect on our rating/rank.
If you have questions, we can discuss them here, or, there is Help chat channel as well. Have a happy Go life.