Polymarket–Betfair Arbitrage: The Overlooked Cross-Venue Routes (2026)

The same real-world events trade on Polymarket as YES/NO contracts settling at $1, and on Betfair as back/lay odds on a betting exchange. When the two venues price an event differently, the gap between a YES contract and a matching lay position opens one of the more overlooked Polymarket Betfair arbitrage opportunities almost nobody is watching for.

Same event, two very different markets

Polymarket prices an event in cents on the dollar. A YES share trading at 37c implies the market sees a 37% chance of that outcome, and a share that resolves correctly pays out $1. Betfair prices the same kind of event in decimal back/lay odds on an exchange, where traders take opposing positions against each other instead of buying contracts.

That is the practical version of the betting exchange vs prediction market distinction: Betfair is peer-to-peer odds trading with a winner and a loser on each side of the same bet, while Polymarket is a direct-settlement contract market where a share simply pays out $1 or nothing. Same underlying event, two different mechanisms for pricing it.

Both formats describe the same thing, a probability, in different units. Converting between them is the first step to spotting a route. The formula: implied probability equals 1 divided by the decimal odds.

The conversion at the common price points:

• Decimal odds 1.50 = 66.7% implied probability = 67c on a prediction market
• Decimal odds 2.00 = 50.0% = 50c
• Decimal odds 3.00 = 33.3% = 33c
• Decimal odds 4.00 = 25.0% = 25c
• Decimal odds 5.00 = 20.0% = 20c
• Decimal odds 10.00 = 10.0% = 10c

Example, not a live quote. Say a will-it-happen event is priced at 44c for YES on Polymarket. On Betfair, backing the same outcome is quoted at decimal odds of 2.10, which converts to an implied probability of 47.6%, or roughly 48c. That four-cent gap between the two venues, before any costs, is the kind of disagreement this article is about.

A worked route: numbers end to end

The figures below are a labeled example, not live quotes, built to show the full calculation.

An event trades at 42c for YES on Polymarket. On Betfair, the same outcome can be laid at decimal odds of 1.60. Laying at 1.60 is equivalent to buying the opposite side at about 37c — it takes the NO side of the same event. Buying YES at 42c and laying the event on Betfair therefore costs roughly 79c against a $1 payout: a 21c gap before fees and slippage.

That 21c has to absorb Betfair's commission before it is real profit. Betfair charges commission only on net winnings in a market, never on a losing bet. Betfair's own charges page bases its worked examples on a 5% Market Base Rate, then applies a Discount Rate tied to the customer's loyalty tier and country. In one of Betfair's own published examples, a customer with a 40% Discount Rate pays an effective 3% (5% x (1 - 40%)) on net winnings. The exact rate a given trader pays depends on their account, region, and Rewards package, so this is a reference point, not a number to plug in blind. On a winning Betfair leg worth roughly 63c, a 3-to-5% commission works out to somewhere around 2c to 3c, which still leaves most of the 21c gap intact in this example, but a trader on a higher rate or with no discount applied would see a meaningfully smaller edge.

For a full breakdown of how a route's combined cost and potential return are calculated on ArbLense, see how routes are calculated.

Why these gaps exist and persist

Polymarket and Betfair pull from largely non-overlapping crowds. Polymarket's volume is dominated by crypto-native traders and US political and macro bettors, while Betfair's exchange runs on a UK and European sports and racing audience with a smaller crossover into politics and current events. When news breaks, the two venues can react at different speeds simply because different people are watching each one.

That is the pattern behind prediction market news arbitrage: the moment one venue's crowd reacts to new information before the other venue's crowd catches up. It is the same underlying mechanism behind polymarket arbitrage between same-category platforms, just applied to a betting exchange rather than another prediction market.

Because the audiences rarely overlap, these gaps tend to close more slowly than gaps between two prediction market platforms that share a trader base, which is part of what makes them worth tracking on their own.

The catches: what eats this spread

Betfair commission. Charged only on net winnings in a market, at a rate set by the trader's country and Rewards tier rather than one number that applies to everyone. Confirm the current rate in-account before counting a route as profitable.

Betfair is not available to US customers. Betfair's exchange does not accept new accounts from the United States, and it withdrew its licensed New Jersey exchange product in 2020. A route that depends on holding a Betfair account only works for traders eligible to hold one, which rules out the largest single pool of US-based prediction market traders. Account access is a separate question from the strategy itself — is arbitrage betting legal covers that split in detail.

Settlement rules mismatch. Polymarket and Betfair each write their own settlement rules, and the wording is rarely identical for the same real-world event. A route only holds if both venues are actually resolving the same outcome under the same conditions. Read both rulebooks before opening either leg.

Currency legs. Polymarket settles in dollars. Betfair accounts are typically held in pounds, euros, or another local currency. Moving funds between the two adds a conversion cost and, if the exchange rate shifts before settlement, a source of profit or loss unrelated to the event itself.

How to hunt these routes

No single tool today scans Polymarket and Betfair together automatically. For now, the workflow is manual: pick an event live on both venues, convert Betfair's odds to an implied cents-on-the-dollar price with the formula above, and compare it against Polymarket's live YES/NO prices. Before sizing anything, check that there is enough liquidity on both legs to actually fill at those prices; a thin order book on either venue can move the price before the second leg is placed, which quietly erases the edge the calculation showed.

That manual check is currently the only way to find real Polymarket Betfair arbitrage opportunities across these two venues. ArbLense's prediction market arbitrage scanner currently covers Kalshi, Polymarket, and Opinion, and does not yet include Betfair.

Whichever direction is being hunted, treat every figure as pre-fee and pre-slippage until both legs are confirmed and commission has actually been subtracted.

Ready to see what the scanner already covers? Scan live cross-venue routes on ArbLense, or open the scanner directly: launch the scanner.