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If Player B were rated 1400, FIDE would calculate one-game Expected Result for Player A as 0.92 (rating difference is more than 400, Player A is stronger). If Player B were rated 2450, FIDE would calculate one-game Expected Result for Player A as 0.08 (rating difference is more than 400, Player A is weaker).

Remember the FIDE rule of 400 points in simple: If the rating difference between 2 players is more than 400, then there are only 2 possible values for the Expected Result. For one game, it is 0.92 for the stronger player and 0.08 for the weaker player.

The Expected Result is important for rating calculation. It is the basis for calculating Rating Increase or Decrease, Rating Change and New Rating. But the Expected Result does not have any impact on the calculation of the Performance Rating, Grandmaster and International Master Norms and Opponents Average.

Rating Increase or Decrease

In the FIDE Players’ Database it is officially called as "change." But let’s name it Rating Increase or Decrease for better understanding. It is an absolute value which can be plus, minus or zero and is calculated as this:

Rating Increase/Decrease = Result – Expected Result

• Example 1: In a 9-game chess tournament Player A scored 5.5 and his Expected Result was 4.0. The Rating Increase/Decrease for player A is therefore calculated as this:
Rating Increase = 5.5 – 4.0 = 1.5

• Example 2: Player A in a 5-game chess event scored 1.5 and his Expected Result was 3.5. The Rating Increase/Decrease for player A is therefore calculated as this:
Rating Decrease = 1.5 – 3.5 = – 2.0

• Example 3: Player A in a 9-game chess tournament scored 4.5 and his Expected Result was 4.5. The Rating Increase/Decrease for player A is therefore calculated as this:
Rating Increase/Decrease = 4.5 – 4.5 = 0

If a chess player has the K-factor 10, then his Rating Change for Example 1 will be 15 (= 1.5 x 10), in Example 2 it will be – 20 (= -2.0 x 10), and in Example 3 it will be 0 (= 0 x 10).

Performance Rating

Performance Rating is very important for calculating and getting the Grandmaster and International Master norms. In FIDE, Performance Rating is calculated with the following formula:

Performance Rating = Opponents Average + Performance Change

Performance Change is based on the Performance Ratio. If a player scored 9 in 9 games, his or her Performance Ratio is 1.00 and Performance Change +800. If he scores 4.5 in 9 games, it is correspondingly 0.50 and Performance Change will be 0. The needed value is taken from the special FIDE Table of Performance Change.

• Example: In a 9-game chess tournament Player A played 9 games with 9 opponents, each opponent was rated 2400 (Opponents Average will be 2400). Player A scored 4.5 (Performance Change will be 0, see above).

In the above example, Performance Rating for Player A is therefore calculated as this:
Performance Rating = Opponents Average + Performance Change
Performance Rating = 2400 + 0 = 2400

In some Chess Organizations (but not in FIDE), the Performance Rating is calculated with "the algorithm of 400": If you win, add 400 to the opponent rating; if lose, subtract 400, if you make a draw, no change. Then find the average.

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