**PLEASE NOTE**: this article has been superseded by an
article
on the ICU ratings web site.

There are two cases: the first for players with an estabilished rating, and the second for players entering the rating pool for the first time.

### Continuous Rating Formula

A rated player's new rating after a rated event is given by the formula

R_{n}= R_{o}+ K(W W_{e})

where

R_{n}is the new rating after the event R_{o}is the old rating before the event K is the rating factor, which determines the maximum change per game W is the actual game score (each win counting 1, each draw 0.5) W_{e}is the expected game score based on R_{o}

The ICU uses four different K values:

K = 40 where rating < 2100 and age < 21 K = 32 where rating < 2100 and age ≥ 21 and playing experience < 8 years K = 24 where rating < 2100 and age ≥ 21 and playing experience ≥ 8 years K = 16 where rating ≥ 2100

A player's expected score, w_{g}, depends on the
difference, R_{d}, between his rating and his
opponent's. If the two players have the same rating then they
each have an expected score of 0.5. As the rating difference
increases, the expected score goes up for the higher-rated
player and down for the lower-rated according to:

w_{g}= 1 / (1 + 10^(R_{d}/400))

The player's expected score for an event, W_{e}, is the sum
of expectations of the individual games:

W_{e}= w_{1}+ w_{2}+ ...

### Performance Rating Formulae

New (unrated) players who enter the rating pool are processed by the Performance Rating Formula for a provisional period.

R_{p}= R_{c}+ D_{p}

where

R_{p}is the performance rating R_{c}is the average competition rating D_{p}is to be read as the difference based on the percentage score P

When sufficient data accrues on their performances against rated players (20 games), subsequent calculations are taken over by the Continuous Rating Formula.