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-3.45Free · Reproducible · Browser-local
Football Elo rating calculator
Calculate one transparent rating update, then replay a full match history without giving simultaneous kickoffs information from the future. Every parameter and boundary stays visible.
Same-kickoff snapshotsZero-sum updatesLeague-isolated replayNo data upload
Browser-local calculation lab
Update one match—or replay a league history
No rows leave this browser. The same versioned engine powers both views, so a worked example and a CSV replay cannot silently use different arithmetic.
Elo expected home score0.673
This is the expected mean of a 1 / 0.5 / 0 result score. It is not a 67% home-win probability and does not define a full 1X2 forecast.
- Actual home score
- 0.5
- Expected away score
- 0.327
- Zero-sum audit
- Pass
- Formula receipt
- football-elo-rating/1.0.0
Interpretation boundary
Elo is a relative rating update rule. This page does not fit K, the home term or season carry; prove those choices out of sample before using ratings in a forecasting system. No output is a pick, price, edge or betting recommendation.
Exact method
Two equations, then strict time ordering
Eₕ = 1 / (1 + 10^−((Rₕ + H − Rₐ) / S))R′ₕ = Rₕ + K(Aₕ − Eₕ) · R′ₐ = Rₐ − K(Aₕ − Eₕ)Eₕ is the home team's expected result score. Aₕ is 1 for a home win, 0.5 for a draw and 0 for an away win. The away update is the exact opposite, so each match is zero-sum. The disclosed defaults are K=20, H=65 rating points and S=400.
The base-10 expectation is an explicitly disclosed adaptation of the FIDE rating-system family. FIDE does not define or endorse this football implementation; the home term, K-factor and season carry are site parameters.
Sort before calculating
Every row is normalized to UTC and sorted by kickoff, then stable match ID. Duplicate IDs and invalid timestamps fail closed before a rating table is published.
Snapshot simultaneous matches
All teams sharing an exact kickoff use ratings from before that group. Updates are applied only after every match in the group has been calculated, so CSV row order cannot leak a result.
Regress once at a season boundary
At the first new-season kickoff, each existing rating becomes base + carry × (rating − base). The default carry is 0.75; returning to an already closed season is rejected.
Use the right next tool
Ratings are one feature, not a forecast
Canonical publication record
Abstract
A deterministic browser-local football Elo calculator for one-match expected result scores and zero-sum updates, plus chronological CSV replay with league isolation, same-kickoff snapshots and explicit season regression.
- Author and publisher
- Football Proof AI
- Publication version
football-elo-rating/1.0.0- Published
- Last modified
- Release status
- Current release
- Review status
- Editorial technical note; not externally peer reviewed
- Production method
- Editorial browser tool maintained from the declared method, linked sources and any listed reproducible artifacts.
- Software and AI assistance
- Software, including generative AI, may assist drafting, transformation or quality checks. It is not treated as a source, author or independent reviewer; factual and quantitative claims must remain bound to cited sources, declared methods or reproducible artifacts.
- Why this exists
- Enable readers to inspect assumptions, reproduce calculations and reject claims that exceed the published evidence.
- Commercial boundary
- No bookmaker, prediction provider or paid placement controls the evidence rules, calculations or conclusions on this page.
- Version history
football-elo-rating/1.0.0: Initial public release.