What does the Elo Rating Calculator work out?

Expected score and rating change for a game of Elo. It is one of the Randomizers & Pickers tools on Mondo Knows.

Do I need to sign up, and is my data stored?

No sign-up, and nothing you type is sent anywhere. The calculation runs in your own browser, so the figures stay on your device and the page works offline once loaded.

Mondo Knows Tools

Elo Rating Calculator

Expected score and rating change for a game of Elo. Use the free elo rating calculator below to get an instant answer, with the formula shown so you can check the maths and trust the result. Free, private, and no sign-up.

Your rating

Opponent's rating

K-factor

Chess uses 10-40 depending on the player and time control.

Result

Mondo says

Fill in the fields, then press Calculate.

How it works

Use it to check what a result should do to your rating before you play, or to see how big an upset you just pulled off. Elo is a model, not a measurement: the K-factor decides how fast ratings move, and official bodies set their own values.

The formula

Expected score E = 1 / (1 + 10^((Ropponent - Ryou)/400)). New rating = R + K x (actual score - E).

Elo Rating Calculator: common questions

What does the Elo Rating Calculator work out?: Expected score and rating change for a game of Elo. It is one of the Randomizers & Pickers tools on Mondo Knows.
How is the Elo Rating Calculator calculated?: Use it to check what a result should do to your rating before you play, or to see how big an upset you just pulled off. Elo is a model, not a measurement: the K-factor decides how fast ratings move, and official bodies set their own values. The maths is short enough to check by hand: Expected score E = 1 / (1 + 10^((Ropponent - Ryou)/400)). New rating = R + K x (actual score - E).
Do I need to sign up, and is my data stored?: No sign-up, and nothing you type is sent anywhere. The calculation runs in your own browser, so the figures stay on your device and the page works offline once loaded.

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Estimates for general guidance only. This is not financial, medical or legal advice. Everything runs in your browser and nothing you type is stored.