Press note
Kalshi–Polymarket Arbitrage: 32,638 Price Checks, and Where a Gap Survived Fees
10.1%Midterm readings that cleared both venues' fees at depth
13,440 readings of 40 matched contracts; the best single reading paid $347.69 on capital held until the result
Vultax matched NFL, college football, Premier League, midterm and Fed contracts on Kalshi and Polymarket and walked both order books every five minutes for 28 hours. Midterm gaps cleared both venues' fees in 10% of readings and a Fed longshot in every one; pre-game sports gaps almost never did. A price gap between Kalshi and Polymarket is easy to find and hard to be paid for. The slower markets were where gaps paid. Midterm contracts cleared fees at depth in 10.1% of readings, and two pairs did so in every reading, the best paying $347.69 on money that stays locked until the election is called. The steadiest edge of all was a quirk of tick sizes on a Fed longshot, worth 0.18% of the capital it needed.
Observed 2026-09-12T18:51Z to 2026-09-13T22:51Z, population: 26,342 readings of matched contract pairs with both order books, excluding in-play sports.
Supporting figures
- 0.18% — The steadiest edge: a tick-size gap on the FedA 50+ bps September hike bid at 1 cent on Kalshi and offered below a cent on Polymarket: a median $714.70 on $325,669, in all 337 readings
- 0 of 7,518 — Pre-game NFL quotes that crossed between venues28 matched game outcomes read every five minutes, 12–13 September 2026
- 16.9% — In-play readings that crossed, then discardedOf 6,296 readings during games; the two venues' books were read up to two minutes apart, so these are timing artefacts
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How to cite
Vultax Research, Kalshi–Polymarket Arbitrage: 32,638 Price Checks, and Where a Gap Survived Fees, 2026-09-16, https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees
Published 2026-09-16. Figures are the published study; live screens move. Plain-text version · Use our data