Elo Rating Calculator
Player A Rating
Player B Rating
Match Result (Player A)
K-Factor
The Elo rating system calculates relative skill levels in two-player games such as chess, football, or tennis. Created by Arpad Elo, it predicts match outcomes and adjusts ratings based on results.
- 1Expected Score: E_A = 1 / (1 + 10^((R_B − R_A) / 400))
- 2New Rating: R_A = R_A + K × (S_A − E_A)
- 3S_A = 1 for win · 0.5 for draw · 0 for loss
- 4K-factor controls volatility — higher K means faster rating changes
Player A 1500 beats Player B 1500 at K=32=A gains +16 to reach 1516, B drops to 1484
Player A 1200 beats Player B 1600 at K=32=A gains ~+29 upset bonus, B loses only ~3
Draw between A 1800 and B 1600 at K=16=A loses ~3 points, B gains ~3
| K-Factor | Used For | Volatility |
|---|---|---|
| 40 | New and beginner players | Very High |
| 32 | Standard club play | High |
| 20 | Intermediate players | Medium |
| 16 | Masters and FIDE rated | Low |
| 10 | Grand Masters | Very Low |
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