Open interest on politics (Polymarket) and sports (Kalshi): 55.3% / 43.6%

Vultax compared Kalshi and Polymarket on structure, fees, holdings and prices. Kalshi and Polymarket list many of the same questions and are different venues underneath. Kalshi is a CFTC-regulated exchange that trades in dollars.

- Taker fee on 100 contracts at 50 cents: $1.00 / $1.75
- Median gap on the exactly matched Fed pair: 574 bps
- Open interest held by the ten largest events: 44% / 49%

Observed 2026-09-13T23:22Z, population: 20,851 open Polymarket events.

Study: https://vultax.com/research/kalshi-polymarket-open-interest-by-category
Markdown: https://vultax.com/research/kalshi-polymarket-open-interest-by-category.md
Data: https://vultax.com/research/kalshi-polymarket-open-interest-by-category/data.json
Share card: https://vultax.com/og/article/research/kalshi-polymarket-open-interest-by-category
Live screen: https://app.vultax.com/analytics/markets

Vultax Research, Where the Money Waits: Polymarket's Open Interest Is 55% Politics, Kalshi's 44% Sports, 2026-09-16, https://vultax.com/research/kalshi-polymarket-open-interest-by-category