Press note
Where the Money Waits: Polymarket's Open Interest Is 55% Politics, Kalshi's 44% Sports
55.3% / 43.6%Open interest on politics (Polymarket) and sports (Kalshi)
$188.9 million of $341.3 million across 20,851 Polymarket events; 453 million of 1.04 billion contracts across 11,715 Kalshi events; 13 September 2026
Vultax compared Kalshi and Polymarket on structure, fees, holdings and prices. On 13 September 2026, 55.3% of Polymarket's $341.3 million open interest sat on politics and 43.6% of Kalshi's 1.04 billion open contracts on sports; on a matched Fed pair in July, prices sat a median 5.7 cents apart. Kalshi and Polymarket list many of the same questions and are different venues underneath. Kalshi is a CFTC-regulated exchange that trades in dollars. Polymarket's main venue is an on-chain order book settled in USDC on Polygon and closed to U.S. residents, with a separate, sports-first U.S. exchange that opened to the public in May 2026. Both charge takers a rate times p × (1 − p): at 50 cents, 100 contracts cost $1.75 to take on Kalshi and between nothing and $1.75 on Polymarket, depending on the category, and Polymarket makers pay no fee.
Observed 2026-09-13T23:22Z, population: 20,851 open Polymarket events.
Supporting figures
- $1.00 / $1.75 — Taker fee on 100 contracts at 50 centsPolymarket's politics rate (crypto $1.75, sports $1.25) against Kalshi's published schedule; Polymarket charges makers nothing
- 574 bps — Median gap on the exactly matched Fed pairAbout 5.7 cents; Polymarket's 4.50% end-2026 upper bound against Kalshi KXFED-26DEC-T4.25, 1,018 observations over 24 hours from 17 July 2026
- 44% / 49% — Open interest held by the ten largest eventsPolymarket and Kalshi, 13 September 2026; led by the 2028 presidential election on Polymarket and the 2028 Democratic nominee on Kalshi
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How to cite
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
Published 2026-09-13, last revised 2026-09-16. Figures are the published study; live screens move. Plain-text version · Use our data