♟️ Elo Rating Update Calculator
Enter two player ratings, choose a K-factor, and evaluate expected scores and rating changes for wins, losses, or draws.
Common: 32 for club players, 16 for masters, 40 for online blitz.
Player A expected score
0.500
Probability of win ≈ 50.0%
Player B expected score
0.500
Probability of win ≈ 50.0%
Result selected
Player A wins
Δ Rating A +16.0 • Δ Rating B -16.0
| Scenario | Score A | Score B | New Rating A | Δ A | New Rating B | Δ B |
|---|---|---|---|---|---|---|
| win | 1.0 | 0.0 | 1516.0 | +16.0 | 1484.0 | -16.0 |
| draw | 0.5 | 0.5 | 1500.0 | +0.0 | 1500.0 | +0.0 |
| loss | 0.0 | 1.0 | 1484.0 | -16.0 | 1516.0 | +16.0 |
How to Use This Calculator
Set current ratings
Enter pre-match ratings for Player A and Player B. Ratings can be from chess, esports, foosball leagues, or any Elo-based system.
Choose the correct K-factor
The K-factor determines rating volatility. Higher K reacts faster to new results; lower K is more stable.
Select the result
Pick win, loss, or draw for Player A to see rating adjustments. The table shows all outcomes for quick what-if analysis.
Apply new ratings
Use the updated ratings to feed into your leaderboard or tournament bracket tracking.
Formula
EA = 1 ÷ (1 + 10(RB − RA)/400)
R'A = RA + K × (SA − EA)
SA = 1 for win, 0.5 for draw, 0 for loss. Player B uses symmetrical equations with EB = 1 − EA.
Elo rating changes reflect performance relative to expectation: beating higher-rated opponents gives large gains, while losing to lower-rated opponents yields larger losses. Draws split the difference.
Strategy & Analysis Tips
Understanding expected score helps you plan tournament strategies. It also reveals rating inflation (consistently winning against underranked players) or deflation (facing overpowering competition).
When to use larger K
- New players whose skill is evolving quickly.
- Online Blitz/Bullet chess or rapid esports seasons.
- Experimental ladders where you want ratings to react faster.
When to use smaller K
- Elite players with established track records.
- Long-running leagues where stability is more important than short-term swings.
- Corporate or school leaderboards to avoid dramatic jumps.
Frequently Asked Questions
Does Elo work for team sports?
Yes. Many leagues adapt Elo for teams by treating each match as a head-to-head contest.
What if players have huge rating gaps?
The logistic formula accounts for large gaps; expected scores approach 1.0 and 0.0, limiting big rating swings on predictable results.
Can I change the 400 divisor?
Yes. Some variants tweak the scaling factor. This calculator uses the standard Elo base of 400.
How often should I update ratings?
After every match. Elo is sequential: each result uses the most recent ratings.
What about provisional ratings?
Use a high K-factor (e.g., 40) for the first 20 games, then switch to the standard K once performance stabilizes.