Where the Money Waits: 55% of Polymarket's Open Interest Is on Politics

Vultax read every open Polymarket event late on 13 September 2026: $341.3 million was open across 20,851 events, and 55.3% of it sat on politics and elections; the economy and the Fed held 16.0%, crypto 12.3% and sports only 7.8%. Holding is not trading: esports was the largest sport by money traded on Polymarket in Vultax's record of 21 August to 12 September, yet it held 0.6% of the venue's open interest, because a match settles within hours.

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. It charges takers a category rate times p × (1 − p): at 50 cents, 100 contracts cost between nothing and $1.75 to take, depending on the category, and makers pay no fee.

What a trader checks before choosing where to trade. Polymarket's taker fee peaks at 50 cents and shrinks toward the ends of the price range, and its rate depends on the market's category.

Open interest is the value of positions still waiting to settle, and it shows where money stays. Vultax paged through every open event on Polymarket's public events endpoint between 23:22 and 23:24 UTC on 13 September 2026. Polymarket reports each event's open interest in dollars.

Polymarket tags events with many labels, so Vultax assigned each event to the first matching group in this order: esports, sports, crypto, economy and Fed, politics and elections, geopolitics, culture, tech; an event tagged both sports and esports counts as esports.

More than half of Polymarket's open money waits on political outcomes, from the 2028 presidential election to Brazil's. The September Fed decision was the second-largest single event by open interest three days before the meeting.

Polymarket's headline trading figures describe fast markets; its open interest describes patient ones. Two examples from Vultax's September measurements show the gap.

• Esports on Polymarket - 21.4% of observed money traded between 21 August and 12 September, 0.6% of open interest on 13 September.
• Crypto up-or-down markets on Polymarket - 59.6% of observed trades in the same window, settling every five minutes to a day, so they barely register in open interest; crypto's 12.3% share is mostly long-dated price questions such as where Bitcoin will trade in 2026.

Open interest is the better guide to what a venue is exposed to and what its users are waiting on. Polymarket's depends heavily on U.S. politics through 2028 and on a handful of events, and it would look very different after the midterms settle. For where daily trading goes, see the up-or-down study and Polymarket's sports and esports markets.

Polymarket operates two exchanges. Its main venue is offshore, while its U.S. exchange, launched in December 2025 on the QCEX designation and opened to the public in May 2026, is sports-first and iOS-only. Since mid-2024 sports has been about 39% of Polymarket's volume, by Pew's count.

Regulation keeps changing who can trade which contract. The Ninth Circuit ruled that federal law does not pre-empt state regulation of prediction markets, contradicting other rulings and pointing at the Supreme Court; Minnesota banned prediction markets from 1 August 2026, and the CFTC has proposed rules barring contracts on injuries and officiating.

Open interest is one reading at one moment. It moves with prices as well as with new positions, and the September Fed event was due to settle on 16 September. Polymarket figures cover its international exchange, not its U.S. exchange. Category groups for Polymarket are Vultax's assignment from Polymarket's tags and would shift slightly under a different order.

Polymarket's fee rates were read from its documentation on 5 September 2026. Nothing here is a recommendation to trade, and nothing here is financial advice. Challenge a figure at [email protected]; material changes are logged in the changelog.