Prediction markets and sportsbooks price the same outcomes — sometimes at meaningfully different prices. When the gap is real, you can hold opposing positions at the two venues and lock in a profit regardless of outcome. This walkthrough is how, with worked numbers.
Why the prices diverge
A sportsbook's futures price on, say, the Chiefs to win the Super Bowl includes a vig margin and reflects mostly US betting flow. Polymarket's contract on the same outcome includes crypto-funded global flow, often institutional, and prices closer to true probability.
When the two prices reflect different audiences and different biases, you can sometimes find:
- The Chiefs at +500 (decimal 6.00) on a US sportsbook (implied 16.7%, devigged maybe 15.5%)
- The Chiefs at $0.14 (implied 14%) on Polymarket
The sportsbook implies a higher probability than the prediction market. Either:
- The sportsbook is over-pricing (vig + US-public bias) and the prediction market is closer to truth, or
- The prediction market is wrong and the sportsbook is right
In either case, if the gap is wide enough, you can hold opposing positions at the two venues and turn the spread into a guaranteed cash position.
The walkthrough — worked numbers
Setup:
- Sportsbook Future: Chiefs to win Super Bowl at +500 → decimal payout 6.00 → implied probability ~16.7%
- Polymarket Contract: Chiefs to win Super Bowl at $0.14 → implied probability ~14%
The sportsbook is paying you more per dollar on the Chiefs winning than Polymarket prices the probability. You're not arbing — you're taking opposite positions:
- Buy Chiefs to win at sportsbook (long the Chiefs)
- Sell Chiefs to win on Polymarket (sell the Yes contract at $0.14)
Sizing the hedge
To lock a profit regardless of outcome, size the two positions so the cash you collect on each outcome is equal (or close).
Stake at sportsbook: $100 on Chiefs at +500.
- If Chiefs win: $100 × 6.00 = $600 collected from sportsbook ($500 profit).
- If Chiefs lose: you lose $100 at sportsbook. On Polymarket, you keep the cash you collected from selling.
To balance, you'd solve for X (Polymarket stake) such that net cash is the same on both outcomes. Solve: $X ≈ $84.
So sell about $84 worth of Yes contracts on Polymarket at $0.14. Net cash position either outcome: about −$16. In this example, the gap is too narrow for a clean profit — but the structure of the trade is what you'd do, and on wider gaps (4%+ implied probability spread) the same structure produces real locked profit.
When this strategy actually works
The gap has to be bigger than the round-trip cost of trading both venues:
- Sportsbook vig (4-5% effective on most futures markets)
- Polymarket settlement risk (small but real — dispute risk)
- USDC bridge fees on Polymarket (~$1-5 per trip)
- Tax friction (different reporting on each)
Realistically, you need a 4-6% implied-probability gap between the two venues before the arb math works clean. Those gaps appear, but they're not constant — you have to scan.
Sharp's market-scanner surfaces these gaps when they appear across the prediction-market / sportsbook universe.
Where the gaps come from
Three recurring sources of meaningful gaps:
- Early-season futures: sportsbooks price futures slowly. Polymarket reprices on every news cycle. A team's odds at a sportsbook can lag Polymarket by 3-5% for weeks after a season starts.
- Public-heavy sides at sportsbooks: a big-brand favorite that the US public hammers gets shorter odds at sportsbooks than its true probability. Polymarket's globally-funded price is often closer to truth.
- Specific high-profile events (Super Bowl winner, NBA champion, NFL MVP) where Polymarket has deep liquidity and the prediction market is the cleaner price reference.
Tax considerations
US tax reporting differs:
- Sportsbook winnings: reported on Form W-2G if you hit thresholds; otherwise self-reported as gambling income.
- Kalshi: regulated futures-style reporting (1099-B treatment in most cases).
- Polymarket: crypto trading reporting via your wallet's transaction history; treat as crypto capital gains/losses for IRS purposes (consult a CPA).
You don't pay tax on a "matched hedge" as a single transaction — each leg is taxed in its own bucket.
The risk to know
Prediction-market settlement disputes are rare but real. If a Polymarket contract gets disputed and re-resolves against your expectation, you can be out the prediction-market leg of your hedge while still holding the sportsbook leg.
Defensive moves:
- Read the resolution criteria carefully on every Polymarket contract before opening a position. Ambiguous criteria = skip.
- Stick to high-volume contracts where any dispute would be widely-watched and less likely to misresolve.
- Don't hedge with size you can't absorb losing the prediction-market side.