Elo & MMR Calculator
See your new rating after a match from your rating, the opponent’s rating and the result, with the expected score and a tunable K-factor. Calculates in your browser.
New rating
-
Show the math
Your expected score depends only on the rating gap, then your rating shifts toward the actual result:
expected = 1 / (1 + 10^((opp − you)/400))
new = rating + K × (actual − expected)
A higher K-factor makes ratings move faster. Chess often uses 10–40; many games use 24–32. The expected score counts a draw as half a point, so it is not a pure win chance.
With FIDE rules on, the expected score comes from FIDE's rating-difference table (which differs from the formula above by up to about 0.02), and a gap of more than 400 points counts as 400 for players rated below 2650, as in the FIDE Rating Regulations from 1 October 2025.
All math runs locally in your browser.
What this does
An Elo & MMR calculator shows your new rating after a match from your rating, the opponent’s rating, and the result, with the expected score and a tunable K-factor.
How to use it
- Enter your rating.
- Enter the opponent rating.
- Pick the result.
- Set the K-factor and read the change.
How it works
Expected score depends only on the rating gap; your rating then shifts toward the actual result by the K-factor. Chess uses 10–40.
new = old + K × (result − expected)
Understanding your result
The rating change depends only on the gap to your opponent, so beating a much stronger player earns far more than beating an equal, while losing to a weaker one costs the most. The K-factor controls volatility: a high K moves your rating fast (good for new accounts finding their level), a low K keeps an established rating stable.
Example
Beating an equal-rated player at K=32 gains about 16 points.
Last updated .
Frequently asked questions
How does Elo work?
Your expected score depends only on the rating gap, then your rating shifts toward the actual result by the K-factor times the difference.
What is the K-factor?
It controls how fast ratings move. Higher values react more quickly; chess often uses 10 to 40 and many games use 24 to 32.
Does it follow FIDE’s chess rules?
Turn on FIDE rules to use FIDE’s expected-score table and its 400-point rule: since 1 October 2025 a rating gap of more than 400 counts as 400 for players rated below 2650. Set K to your FIDE value (40, 20 or 10).
Is my data kept?
No. Everything is computed locally in your browser.
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