FIDE Elo Rating Change Calculator

How FIDE Elo Rating Changes Work

The FIDE rating system, developed by Professor Arpad Elo in 1960, calculates rating changes based on the difference between your rating and your opponent's rating. After every rated game, your Elo adjusts up or down depending on the result vs. expectation.

The Elo Formula Explained

Your expected score E = 1 / (1 + 10^{(R_opponent−R_player)/400}). If you are rated 400 points higher than your opponent, your expected score is about 0.91 (you should win 91% of the time). Your rating change Δ = K × (Actual Score − Expected Score). A win = 1.0, draw = 0.5, loss = 0.0.

K-Factor Guide (Updated 2024)

• K = 40: New players with fewer than 30 rated games, and all players under 18 rated below 2300.
• K = 20: Players rated below 2400 who have completed at least 30 rated games.
• K = 10: Players who have ever reached 2400+ rating, even if their rating later drops below 2400.

Example Calculation

You (rated 1800, K=20) play someone rated 1900. Expected score = 1 / (1+10^{(1900−1800)/400}) = 0.36. If you WIN: Δ = 20 × (1.0 − 0.36) = +12.8 → +13 Elo gained. If you LOSE: Δ = 20 × (0 − 0.36) = −7.2 → −7 Elo lost. A draw gives +2.8 → +3.

Tournament Rating Calculation

For multi-game tournaments, calculate each game individually and sum the changes. Your resulting rating is: R_new = R_old + sum of all Δ values. Always use your rating at the start of the tournament for all calculations — FIDE does not recalculate between rounds.

Frequently Asked Questions