Groups Polymarket group-winner odds · click 1/2/3/4 to force a finish
Inline notes
Each team's group-winning probability comes from Polymarket's "Group X Winner" market (or a fallback prior if the API is unreachable).
By default the simulator just uses those odds. To force a specific scenario, click 1 / 2 / 3 / 4
next to a team to lock its group finish (1st / 2nd / 3rd / 4th); click the same button again to unlock.
For full documentation, click the README button up top.
Click match → see who can play itEach card: reach% (team appears here) · win% (head-to-head vs the other team on this card — the two win%s sum to 100)The favored team in each match (marked with ▸) flows into the next round
WC26 Bracket Engine
A probability sandbox for the 2026 FIFA World Cup knockout stage
What this is
An interactive simulator for the entire knockout stage of the 2026 FIFA World Cup — from the Round of 32 through the Final.
For any match in the bracket, it tells you which teams are most likely to play in it, with what probability, and how each
pairing would resolve. Originally built to answer a practical question: which teams could realistically end up playing
the Round of 16 match in Seattle on July 6 (Match 94)?
Where the numbers come from
Group stage odds: Pulled live from Polymarket's Group X Winner prediction markets via their public Gamma API.
Each team's market-implied win probability becomes their strength. If the API can't be reached from your browser
(CORS or network), pre-loaded fallback priors based on FIFA rankings are used.
Finish probabilities: Win-% gives 1st-place probability directly. Runner-up, 3rd-place, and elimination
probabilities are derived using a Plackett-Luce
sampling model: draw the standings 1→4 by sampling without replacement weighted by team strength.
Knockout matches: Each pairing's outcome uses the same odds-based formula —
P(A wins) = sA^v / (sA^v + sB^v), where v is the Variance exponent. Lower variance produces more upsets;
higher variance favors chalk.
3rd-place routing: All 495 combinations from Annex C of FIFA's official tournament regulations are
baked into the simulator. So when a sim lands on a particular set of 8 qualifying 3rd-place teams, the lookup
deterministically routes them into the correct Round of 32 slots — not a random guess.
How the simulation runs
Each click of ⟳ Re-Simulate runs N Monte Carlo simulations of the full tournament
(default 10,000; configurable from 500 to 100,000). For every sim it: samples each group's final standings, identifies the
8 best 3rd-place teams, applies the Annex C lookup to assign R32 matchups, then plays out R32 → R16 → QF → SF → Final
one match at a time. Results are aggregated across all N sims to produce probabilities for each slot in the bracket.
What the controls do
Lock a team's group finish: Click 1 / 2 / 3 / 4 next to any team to lock that team to
that group placement (1st / 2nd / 3rd / 4th) in every simulation. Click the same button again to unlock. Each placement is
unique within a group, so locking a new team to a placement clears the previous holder. By default no team is locked and
the simulator just uses the Polymarket odds.
Force a match winner: Click any bracket match to open its detail panel, then use the "Force winner" buttons to
lock a team to win that match. The downstream bracket re-simulates with that constraint.
Variance: 0.5 = maximum chaos (Cape Verde might really beat Spain). 1.0 = pure odds. 0.85 (default) is a
historically calibrated middle ground for knockout football.
Sims: More sims = more precise probabilities, slower re-render. 10k (default) is snappy and accurate enough for
most questions; bump to 50k or 100k for tighter tail estimates if you can wait a couple of seconds.
Refetch odds: Pulls the latest Polymarket prices without clearing your locks.
Reset all: Wipes overrides and locks, refetches live odds, re-runs the sim from scratch.
Reading the bracket
The bracket is laid out March-Madness-style: Round of 32 on the far left and right, fanning inward through R16 → QF → SF
to the Final in the center. The 3rd-place playoff sits below the Final.
The bracket shows a single most-likely path: the favored team in each match (marked with a red
▸) flows into the next round, so it reads like one filled-in bracket rather than a
jumble of independent match-ups. Each card shows two numbers per team: reach% · win%.
reach% is how often the team appears in this match across all sims. win% is the head-to-head conditional —
when those two specific teams actually meet here, what fraction of the time each one wins. The two win%s sum to 100%
(they're the only two outcomes when those teams meet), and the higher win% is always the marked advancer.
Example: a card showing Belgium · 42% · 53% and Norway · 38% · 47% means Belgium reaches this
match in 42% of sims, Norway in 38%, and on the occasions they actually meet here Belgium wins 53% of the time and Norway
47%. For R32 matches the slot is deterministic from group standings, so only the reach% (finish probability) is shown.
Because it's one representative path, the cards under-state the chaos — a 25% favorite still loses most of the time. The
detail panel (click any match) keeps the full picture: every team's odds of reaching that match and the top
head-to-head pairings.
Reading the detail panel
Click any match to open it. The right panel shows:
Teams most likely to play in this match, ranked by probability.
Top 10 pairings for this match, with the head-to-head win split for each.
Force-winner buttons to lock any of the top 8 candidates to win this specific match.
Known caveats
The "which 3rd-place teams qualify" ranking uses team strength as a proxy. Real life uses points → goal difference → goals scored.
This biases qualification toward favorites, which slightly shrinks tail outcomes.
Polymarket markets close ~June 27 (group-stage end). After that point, market prices stop updating and the app falls back to
whatever the last-fetched values were.
Knockout draws and ties are not modeled separately — every match is decided as a single Bernoulli trial.
Extra time + penalties are absorbed into the win probability.