Cross-Market Arbitrage
How to find and exploit price discrepancies between prediction markets, sportsbooks, and exchanges.
The same real-world event can be traded on a prediction market (Polymarket, Kalshi), bet on at a sportsbook (DraftKings, FanDuel), or hedged on an exchange (Betfair, Smarkets). Each venue prices the event independently, using different models, different customer bases, and different fee structures. When those prices disagree by more than the combined transaction costs, you have a cross-market arbitrage—a way to lock in profit regardless of the outcome.
How Cross-Market Arbitrage Works
The principle is identical to traditional sports betting arbitrage: buy "yes" on one venue where the price is low, and buy "no" (or lay) on another venue where the "yes" price is high. If the combined cost of both sides is less than $1.00 per contract, the difference is your locked-in profit.
You buy YES on Polymarket for $0.58. You bet the equivalent NO on a sportsbook where the NO side implies $0.38 cost. One side wins $1.00, the other loses its stake. Your locked-in payout is $1.00, your total cost is $0.96, and your profit is $0.04 regardless of outcome.
Good to Know
Where the Price Discrepancies Come From
Prediction markets and sportsbooks have structurally different pricing dynamics:
Venue Pricing Differences
| Factor | Prediction Market | Sportsbook | Implication |
|---|---|---|---|
| Pricing mechanism | Order book / AMM | Market-maker sets lines | Different price discovery speed |
| Customer base | Traders, analysts, political junkies | Sports bettors, recreational | Different information sets |
| Fee structure | 1–2% on winnings (varies) | 5–10% vig built into odds | Sportsbooks need wider spreads |
| Liquidity | Varies (thin in niche markets) | Deep for major events | Prediction markets may lag |
| Regulation | CFTC (Kalshi), offshore (Polymarket) | State gaming commissions | Different product offerings |
Structural differences create persistent pricing gaps
Practical Examples
Politics: Presidential Election
Prediction markets often price political outcomes differently from offshore sportsbooks:
- Polymarket prices Candidate A at 58 cents (58% implied)
- An offshore sportsbook has Candidate B at +130 (43.5% implied)
- Total implied: 58% + 43.5% = 101.5%—no arb (you need <100%)
- But if the sportsbook offers Candidate B at +150 (40% implied): 58% + 40% = 98%. That is a 2% arb.
Sports: Sportsbook vs. Prediction Market
Some prediction markets offer sports outcomes that overlap with sportsbook lines:
Thin, but real. Cross-market sports arbs are typically smaller than political ones because sports pricing is more efficient. You need volume and low transaction costs to make it worthwhile.
Accounting for Fees and Commissions
The naive arb calculation above ignores transaction costs. In reality, you must account for:
Fee Structures by Venue Type
| Venue | Fee Type | Typical Rate | Impact on Arb |
|---|---|---|---|
| Polymarket | None on trades (as of 2025) | 0% | Best for arb seekers |
| Kalshi | Commission on winnings | ~1% | Reduces effective payout by 1% |
| US sportsbook | Vig built into odds | 4–10% | Already reflected in the line you bet |
| Betfair Exchange | Commission on net winnings | 2–5% | Reduces effective payout on winning side |
| Wire transfer / crypto gas | Deposit/withdrawal fees | Variable | Adds fixed cost per arb cycle |
Always calculate post-fee returns before executing
Commission is charged only on the winning side, and you do not know which side wins. The expected fee impact is: win probability × commission rate on each side, summed. For a ~50/50 event with 1% commission on one side: 50% × 1% = 0.5% expected cost.
Strategy Insight
Execution Challenges
Timing Risk
Cross-market arbs require executing on two different platforms. In the 30–60 seconds between your first and second trade, prices can move. The arb that existed when you checked may be gone by the time you execute the second leg.
Liquidity Constraints
Prediction market order books may be thin. A $0.58 bid for 100 contracts does not mean you can buy 10,000 contracts at that price. Large orders move the market and destroy the arb.
Capital Lockup
Prediction market contracts may not settle for months. Your capital is locked in a 3% arb for 6 months, which is only 6% annualized. That opportunity cost matters.
Counterparty and Settlement Risk
Offshore prediction markets and sportsbooks carry counterparty risk. If one venue fails to pay out, your "guaranteed" arb becomes a one-sided loss.
Regulatory Considerations
Cross-market arbitrage raises unique regulatory questions:
- US prediction markets (Kalshi) are regulated by the CFTC as event contracts. State sportsbooks are regulated by gaming commissions. Using both is legal, but each has its own compliance requirements.
- Offshore prediction markets (Polymarket) operate outside US regulation. Using them alongside US sportsbooks creates potential legal ambiguity depending on your jurisdiction.
- Tax reporting differs by venue type. Prediction market gains may be reported as capital gains; sportsbook winnings are gambling income. Consult a tax professional.
Warning
Strategy Insight
Sources & References
- Arbitrage pricing theory: low-variance return exists when the cost of covering all outcomes sums to less than the locked-in payout. Standard financial mathematics, independently verifiable.
- Polymarket Docs, Kalshi Rule Filings (CFTC). Prediction market pricing mechanisms (AMMs, order books) and their structural differences from sportsbook market-making are documented in platform technical documentation.
- Rothschild, D. (2009). "Forecasting Elections: Comparing Prediction Markets, Polls, and Their Biases." Public Opinion Quarterly.. Cross-market efficiency and pricing discrepancies between prediction markets and sportsbooks for political events have been studied empirically.
- Commission structures and fee schedules sourced from published terms of service for Kalshi, Polymarket, Betfair, and major US sportsbooks as of early 2026.
Mathematical claims are independently verifiable. BonusBell platform analysis reflects data from 220+ tracked platforms as of March 2026.
Key Takeaways
- 1Cross-market arbs exploit price differences between prediction markets, sportsbooks, and exchanges for the same event
- 2Structural differences in pricing mechanisms, customer bases, and fee structures create persistent (not random) discrepancies
- 3Always calculate post-fee net returns — many apparent arbs disappear once commissions, vig, and transfer costs are included
- 4Execution risk (timing, liquidity, capital lockup) is the primary practical challenge; the math is simple but the execution is not
- 5Understand regulatory and tax implications before mixing CFTC-regulated prediction markets with state-regulated sportsbooks