What is an MMR / Elo rating?

An MMR (matchmaking rating) or Elo rating is a single number that estimates a player's skill from their results. Beat someone stronger and you gain more points; lose to someone weaker and you drop more. RallyMouuu starts every player at 1000 and updates the number after each submitted game.

How an Elo rating updates

Elo compares the two sides before a game and turns the gap into an expected result — a win probability. If you were expected to win and you do, your rating barely moves; if you were the underdog and win, it jumps. Every point one side gains is taken from the other, so the system is zero-sum.

The exact maths RallyMouuu runs

Rally uses a standard, margin-aware Elo. For a game between side A and side B:

Everyone starts at the 1000 baseline, and games are replayed in the order they were submitted — so the board is a deterministic function of your recorded results, not a live guess.

Doubles: how a side’s rating works

In 2v2 (or any multi-player side) a side’s rating is the meanof its members’ ratings. The single Δ from the game is then applied to every member of that side — so partnering a stronger player and winning still earns you rating, and the maths never double-counts.

Why ratings never combine across sports

A session is always one sport, and each sport keeps its own separate ladder. Your badminton rating and your pickleball rating are independent numbers — a strong badminton MMR gives you no head start in pickleball.

MMR vs Elo — is there a difference?

In casual use they mean the same thing: a skill number that updates from wins and losses. “Elo” is the original chess-rating formula; “MMR” (matchmaking rating) is the game-world name for the same idea. RallyMouuu runs Elo maths and labels the result MMR.

Next: what a ladder ranking is, solo vs pairs vs team boards, or the glossary.