Expected score & rating change
Your win/draw/loss odds against any opponent, and exactly what a win, draw or loss does to your rating.
OpenFree chess calculators
The rating math, on sliders
The numbers behind your chess, made playable: every assumption on a slider, a live chart, and an honest note on what actually moves the result. 11 tools and counting.
Rating & Elo
The math behind your number: your odds against any opponent, what each result is worth, and where your results are really heading.
Win probability & odds
Turn a rating gap into a probability and plain odds — and see why the curve is an S, not a line.
OpenExpected points over a run
Your most likely total over N games at a given rating gap, plus the honest spread around it.
OpenPerformance rating
Turn a tournament score into the rating you actually played at — the number a good event is really worth.
OpenRating goal planner
How many games your current results imply to reach a target — and the rating ceiling those results set.
OpenTournaments & results
Planning a run and reading a streak: what you still need from an event, and how a sequence of results moves your rating.
Tournament score planner
Rounds left, points to go, and the exact score rate that reaches your target from here.
OpenResults-streak rating tracker
Build a run of wins, draws and losses and watch your rating bend toward the level they justify.
OpenTiebreak calculator
Buchholz, Median-Buchholz and Sonneborn-Berger from your opponents and results.
OpenRating systems
Beyond plain Elo: the modern system that also tracks how confident it is about your number.
Endgames
The exact, learnable rules that decide a king-and-pawn ending — playable, not just described.
Want to put these numbers to work? Play a rated game or work through the Learn track.