# Calculation of national rating

In order to calculate effect on national rating, should it be enough to choose the relevant k coefficient (assuming this is what makes for the discrepancy between national rating and FIDE rating) and plug it in here: https://ratings.fide.com/calculator_rtd.phtml ?

Furthermore, is there a resource out there to find k coeffients per country (I'm located in Israel, so if anyone knows that specifically, even better).

• Well, yes, if your assumption is correct. No, if it isn't. The question you really seem to be asking is: "How do I calculate national rating in Israel?" For that you should go to the website of Israeli Chess Federation and check what rules they have for calculating national ratings. This should work for any country as long as those documents are public (and why wouldn't they, right?). – IA Petr Harasimovic Aug 4 '18 at 20:03
• @IAPetrHarasimovic ... and as long as you can read the language :-} – Brian Towers Aug 4 '18 at 23:15

In order to calculate effect on national rating, should it be enough to choose the relevant k koefficient (assuming this is what makes for the discrepancy between national rating and FIDE rating) and plug it in here: https://ratings.fide.com/calculator_rtd.phtml ?

No. For the simple reason that countries use different methods for their rating/grading system. Some use an elo system others don't. England, for instance, uses a completely different system.

If you go to the ECF grading website and click on help, on the left hand side of the page, then towards the bottom of the help there is a section describing how the ECF calculate their grades.

The basic method of calculation is as described in the next few paragraphs. For juniors, however, there are differences as described further down.

Points are allocated in respect of each game. For a win you score the opponent's grade plus 50, for a draw the opponent's grade, and for a loss the opponent's grade minus 50. "Grade" means his grade current at the time of grading. There is a proviso that if your opponent's grade differs from yours by more than 40 points it is assumed to be exactly 40 above (or below) yours. This applies whatever the result.

If an opponent (or the player himself) is ungraded, a "starting grade" is estimated, using all available information. See Estimating a starting grade for an ungraded player below. Note that FIDE ratings are ignored. An opponent who has only a FIDE rating will be treated as ungraded.

In the interval between the end of a grading period and publication of the new grades, the "current" grade for calculation purposes is the new, as yet unpublished, grade.

The grade is calculated by dividing the total number of points scored by the number of games played. If there are 30 or more games in the most recent 12 months, then the grade is based on these games alone. If there are not, it is based on the most recent ** 30 games played; or on all the games played in the last 36 months if that is less. In no case does calculation go back more than 36 months. Where games are brought forward from a previous period, they are not recalculated. The number of points scored for a game always remains the same.

** "Most recent" has a special meaning here. In principle the program counts backwards till it reaches 30 games. But there are certain disadvantages (see Appendix) to applying this naïvely. Instead, if the 30th game falls part way through a 6-month period, the program will take as many games from that period as it requires in order to make up the 30; but they will be notional games calculated at the average score for the whole 6-month period.

How is "most recent 30" interpreted if a game has been reported late and graded in the "wrong" period? Answer: the game will be listed under the grading period in which it was reported and calculated, and it will go into that period's grade with a notional playing date of 1st January (or 1st July as the case may be). This notional date will be used, where necessary, to determine the game's position in the backward count to 30.

Rounding
Grades are calculated to the nearest whole number (halves go up). Rounding is done once, at the end. A grade, once rounded and published as a whole number, is henceforth deemed to be that whole number.

You say -

I'm located in Israel, so if anyone knows that specifically, even better

Really? Do you play chess in Israel? Do you have an Israeli rating? Can you read Hebrew?

I'm guessing some of the answers must be "No" since otherwise you would be better placed than 99.9% of forum members to find out the information for yourself and are only asking out of sheer laziness.

My ICF rating is in the 1800's and my k factor is 12.

Boris Gelfand's ICF k factor is 10 as you can see from the calculations for his Israeli rating from his games played abroad (i.e. converting his opponents' FIDE ratings to ICF and then using them to calculate changes to Gelfand's Israeli rating). This link takes you to Gelfand's ICF rating page and then you will have to click on משחקים בחו"ל (middle / fourth of the box links underneath his main details).

Here is the same page for Liel Levitan, the European Schools girls U7 champion. Her Israeli rating is 1445 and her k factor is 14. Again, on the page click on משחקים בחו"ל to get to the calculation page.

Here is the Israeli rating list (but I don't understand why you couldn't get this for yourself if you are living and playing in Israel?) You can find players of different strengths and ages and check their k factors. I know the ICF website is hard to navigate. I found the old one from about 5 years ago much easier. It used to give the calculations, including k factor, for every game, not just the foreign ones, so including the Israeli ones.

As you can see from the FIDE Ratings Change Calculator you cannot type in any k factor. That means that in general you cannot use this for ICF ratings and for other federations only if they use the same k factors.

• let's try to keep the tone here in the forum civil and polite, and not assume that questions are asked out of "sheer laziness". I figured probably questions of conversion of different national rating arise quite frequently and thus there might be a resource that provides info on the calculations per country. As for your answer, you did find the k factor under the tab of "games played abroad", it's still unclear what about games played locally. – acye Aug 5 '18 at 4:52
• I upvoted for the links to the right website and explaining the `K` factors. However, you did not really answer the question whether if you know `K` you can use the FIDE calculator. That's the important question, I think. – IA Petr Harasimovic Aug 6 '18 at 0:33
• @IAPetrHarasimovic I gave the example the OP asked for of the Israeli Chess Fedreation and showed that k factors of 10, 12 and 14 are used (possibly there are more). If you go to the FIDE rating website you see that 12 and 14 are not options you can choose for k. Therefore the answer is the one I gave of "No". – Brian Towers Aug 6 '18 at 10:57
• @BrianTowers Thanks, the last paragraph made it clear, I did not really pay attention to what inputs the calculator allows. I was more thinking whether the choice of `K` is the only difference. – IA Petr Harasimovic Aug 6 '18 at 12:47

What I can recommend myself is to "backtrack" the k coefficient based on historical rating changes. For example, if you know that after a certain game your national rating changed by X points, and you know what rating you and your opponent had before the game, then you could plug that data into the FIDE calculator and try for different values of k to find out what k factor your national rating is based on (assuming it's one of the values that FIDE allows in the dropdown in the calculator).

Otherwise, it's of course also possible to do the same by using the actual ELO equation which is easily Googled or found on Wikipedia.

One word of caution, though: the pre-game rating of the players may be slightly different compared to the last time rating were published, let's say if ratings are published at the beginning of each month and the game took place mid-month after the players had already played a few games and rating changes took place.

• I feel like you're begging the question here. OP asks if you can use the FIDE ratings calculator if you know K, and you suggest to use the FIDE ratings calculator to find K. That only works if the answer to his question is "yes". Even if that's the case (which you can't just assume) K can change based on several factors - heck, in the USCF it changes based on how many games you played in a particular tournament; shorter tournaments have higher K. So even if your derived value was correct, it might not be accurate if applied to other tournaments or players. – D M Aug 7 '18 at 14:54
• @DM - I asked two questions, my answer here was to the 2nd question, about a resource to find k per nation. However, you have a valid point and provided valuable info that I did not know, regarding what you wrote about k changing in certain countries (the US in this case). – acye Aug 7 '18 at 16:33