1. What is the ELO Expected Score?

The ELO expected score represents the probability of a player winning against an opponent based on their respective ELO ratings. It's a fundamental component of the ELO rating system used in chess and other competitive games.

2. How Does the Calculator Work?

The calculator uses the ELO expected score formula:

Where:

• \( E \) — Expected score (probability of winning)
• \( R \) — Your ELO rating
• \( R_{opp} \) — Opponent's ELO rating

Explanation: The formula calculates the expected outcome of a match between two players based on their rating difference. A 400-point difference means the higher-rated player is 10 times more likely to win.

3. Importance of Expected Score

Details: The expected score is used to determine rating changes after games. If you perform better than expected (score > E), your rating increases; if worse, it decreases.

4. Using the Calculator

Tips: Enter both players' ELO ratings. The result will be your expected score against that opponent (a value between 0 and 1).

5. Frequently Asked Questions (FAQ)

Q1: What does an expected score of 0.75 mean?
A: It means you have a 75% chance of winning (or expected to score 0.75 points in a game where wins=1, draws=0.5).

Q2: Why is 400 used in the formula?
A: The 400-point scale is a convention that makes ratings meaningful - a 400-point difference means 10:1 expected score.

Q3: Can expected score be greater than 1?
A: No, it's always between 0 and 1, representing probability.

Q4: How is this different from win probability?
A: In chess, expected score accounts for draws (e.g., 0.75 might mean 50% win, 50% draw, 0% loss).

Q5: Does this work for team ratings?
A: Yes, the same formula can be applied to team ELO ratings.