Elo Rating Calculator
Explore expected score and a one-game rating change. Adjust the ratings, result, and K factor to understand the mathematics.
This is not an official FIDE calculator. It does not implement all official rating tables, initial-rating rules, eligibility, caps, rating-period aggregation, or rounding rules.
The formula
Expected score = 1 ÷ (1 + 10((opponent rating − your rating) ÷ 400)).
Rating change = K × (actual score − expected score). Estimated new rating = starting rating + rating change.
Read the result correctly
Expected score is not the same as a pure probability of winning: draws contribute half a point. The K factor controls how responsive the illustrative update is. A larger K produces a larger change for the same surprise result.
Sources & further reading
References checked September 5, 2026. Linked services are independent of ChessRankings.com™.