Season-end projections for Italian football leagues: a league-table simulator with official tie-break rules, retrospective validation and per-league calibration

We describe the league-table simulator published by calcio.it for 16 Italian leagues (Serie A, Serie B, the three groups of Serie C, the nine groups of Serie D, and the women's Serie A and Serie B). It has two functions: a deterministic “what if” table, in which the reader chooses the results of the remaining matches, and season-end probabilities for every team. Both rest on the same rules engine, which applies the official 2026/27 tie-break rules of each league and declares play-off matches instead of resolving them. Recomputed from results over 207 comparable past seasons, the engine shows no difference in the order of teams level on points that is attributable to it. Probabilities come from a Poisson goals model with estimation uncertainty and 10,000 simulated seasons per league. A league publishes probabilities only if, measured retrospectively over its own archive (231 seasons, 764 evaluations at four points of the season), the model’s ranked probability score is lower than that of a historical-frequency reference. All 16 leagues pass, with skill between 13% and 75%; four are kept without probabilities for editorial reasons stated in the note.