Midterm readings that cleared both venues' fees at depth: 10.1%

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. The slower markets were where gaps paid.

- The steadiest edge: a tick-size gap on the Fed: 0.18%
- Pre-game NFL quotes that crossed between venues: 0 of 7,518
- In-play readings that crossed, then discarded: 16.9%

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.

Study: https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees
Markdown: https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees.md
Data: https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees/data.json
Share card: https://vultax.com/og/article/research/kalshi-polymarket-arbitrage-gaps-after-fees
Live screen: https://app.vultax.com/predictions

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