Is there arbitrage between Kalshi and Polymarket?
Much less often than the price gaps suggest. Right now MarketMaster is tracking 0 cross-venue edges where the same event is priced on both Kalshi and Polymarket. The average gap is — raw — 0 of 0 are still non-negative after fees, and 0 carry resolution deadlines that disagree between the two venues, which makes them not arbitrage at all.
Today's widest gaps, before and after fees
| Market | Venue | Side | Raw edge | After fees |
|---|---|---|---|---|
| No cross-venue edges on the board this minute. The engine recomputes every ten minutes. | ||||
Live, unfiltered, in the order the engine ranks them. Nothing here is a recommendation, and an edge that survives fees can still fail on depth — see below.
The four things that eat a cross-venue edge
1. Fees
Kalshi charges a trading fee that scales with price and contract count; Polymarket's costs show up in the spread and in gas. A gap quoted gross is not a gap you keep. On the live board above, fees alone move the average edge from — to —. There is a fuller breakdown on the venue comparison.
2. Depth
The top of the book is not the size you can fill. An edge measured against the best ask usually shrinks as you walk down the ladder, and on thin markets it can vanish in the first few hundred dollars. MarketMaster reports edge at the ask and edge at size for this reason.
3. Settlement dates that disagree
Two venues can list what looks like the same question and resolve it on different dates, against different sources. 0 of the 0 live pairs are flagged that way right now. A spread between contracts that settle differently is not arbitrage — it is two different bets.
4. Markets that are not the same market
The hardest one. "Will X happen by June 30" and "Will X happen by July 31" look almost identical to a naive matcher, and so do two meetings of the same teams on the same day. Every false match manufactures a spread that does not exist. Matching on venue identifiers rather than on title similarity is how MarketMaster avoids most of it, and mismatches that do slip through are what the settlement check catches.
How these numbers are produced
MarketMaster ingests both venues every few minutes, matches the same event across them, compares the stated resolution terms, and prices the difference after fees and depth. The board above is the same data the scanner and the public API serve. Method notes are on the methodology page.
Prices move constantly. Anything quoted from this page is a snapshot; the API is the current source of truth.