Before a tournament, most players ask the same question: how many rating points can I win or lose? The answer comes from one short formula, and you can work it out yourself in under a minute. Or skip the maths and use our free chess Elo calculator.

Step 1: Expected score

Your expected score against an opponent depends only on the rating gap:

E = 1 / (1 + 10^((opponent − you) / 400))

If you are equal, E is 0.5. A 100-point favourite is expected to score about 0.64. A 200-point favourite, about 0.76. The expected score is not the chance of winning; it counts a draw as half a point.

Step 2: Rating change

change = K × (actual score − expected score)

K is the "volatility" factor. FIDE uses:

  • K = 40 for new players (first 30 games) and juniors under 18 rated below 2300
  • K = 20 for players under 2400
  • K = 10 for anyone who has ever reached 2400

National federations such as USCF and the ECF use their own systems, so treat the result as an estimate.

A worked example

You are rated 1500 with K = 20 and you play a 1600-rated opponent. Your expected score is about 0.36. If you win, you gain 20 × (1 − 0.36) = 12.8 points. If you draw, you gain about 2.8. If you lose, you drop about 7.2.

Notice the asymmetry: beating a stronger player pays much more than losing to one costs. That is the whole idea of the system.

Performance rating

Performance rating answers "what rating did I effectively play at?" Take the average rating of your opponents and add a rating difference based on your score percentage from the FIDE table. Scoring 50% gives a performance equal to your opponents' average. Scoring 75% adds 193 points, and scoring 90% adds 366.

Be careful with short events. A 3-round tournament can produce wild performance numbers. They get meaningful around 7 to 9 games.

Planner and rating history

The Planner tab answers "what do I need?". Enter the opponents you expect and a target such as +10, and it shows the minimum score required, plus your rating change and performance for every possible score. Sign in and use Save to my history to keep each tournament; your rating history is charted over time so you can see real progress.

The calculator also applies the FIDE rule that rating differences above 400 count as 400, which you can switch off for other systems.

Use it for planning

Enter your rating, your K-factor and a list of opponents with results, and the Elo calculator shows each game's change, your total change, your new rating and your performance rating. Try "what if" scenarios before round 1: what happens if you score 50% against a higher-rated field? You might be pleasantly surprised.

Then look at the tournaments coming up on Chess Home events and see where you would seed.

Official changes depend on your federation's rules, such as rating floors, provisional ratings and rating-period updates.