What do people bet on? 24-hour volume by category on Kalshi and Polymarket

Prediction markets are mostly sports and politics, but the two biggest platforms have very different mixes. We took every open market on Kalshi and Polymarket on 30 October 2026 and added up the trading of the previous 24 hours by category. On Kalshi, sports made up 47.8% of volume and politics 39.4%. On Polymarket's international site, sports were 27.0%, politics 26.1%, geopolitics 18.7% and crypto 13.7%.

Inside sports the differences are even sharper. On Kalshi, tennis, golf and college football led; on Polymarket, soccer and esports. And on both platforms a tiny share of markets did almost all the trading.

Key findings

• Kalshi traded about 101 million contracts in 24 hours: sports 47.8%, politics 39.4%, crypto 5.8%, economy 3.3%, culture 2.4%.
• Polymarket's international site traded about $65.3 million: sports 27.0%, politics 26.1%, geopolitics 18.7%, crypto 13.7%, economy 6.6%.
• Tennis (22% of Kalshi's sports volume), golf (17%) and college football (16%) led Kalshi's sports trading; soccer (30%) and esports (29%) led Polymarket's.
• The top 1% of open markets carried 90% of Kalshi's volume and 94% of Polymarket's.
• Only 14.6% of Kalshi's open markets and 8.3% of Polymarket's traded at all that day.

How we did it

We grouped categories into nine buckets: sports, politics (including elections), geopolitics, crypto, economy (economics, financials, companies, commodities), culture (entertainment and "mentions" markets), weather, tech and AI, and other. Polymarket events can carry several tags; we assigned each to one category in a fixed order, with sports first and politics last, so an event tagged both "politics" and "geopolitics" counts as geopolitics.

Kalshi counts volume in contracts and Polymarket in dollars, so we compare shares within each platform, not totals across them. The category table is in the open data file.

What is in each category

Kalshi: sports and politics are 87% of trading

Sports and politics together made up 87% of Kalshi's volume. Politics was unusually high because of the midterms: the single busiest market was Ken Paxton in the Texas Senate race, with about 3.1 million contracts, followed by the Republican side of the House control market (2.8 million) and four outcomes of the balance of power combination market.

Because Kalshi counts contracts, cheap long-shot contracts weigh as much as expensive ones. As a check, we weighted each contract by the smaller of its "Yes" and "No" prices, a rough measure of money at risk. Sports rose to 53.6% and politics was 38.3%, so the picture holds.

Polymarket: a more even mix

Polymarket's international site is far less concentrated in sports. Geopolitics, almost absent from Kalshi, was nearly a fifth of its volume, led by Israel's prime minister market ($1.2 million on Benjamin Netanyahu) and a market on whether the US–Iran ceasefire lasts through 31 October ($0.84 million). Crypto price markets were 13.7%, more than twice Kalshi's share.

Politics was still big: the Republican side of the House control market was Polymarket's busiest outcome at $2.3 million, followed by the Republican side of Senate control at $1.4 million.

Which sports?

The two platforms' sports businesses barely overlap:

• Kalshi's sports trading is mostly American. College football, the NFL and the NBA made up over a third of its sports volume. Tennis led, at 22%, from hundreds of ATP, WTA, Challenger and ITF matches; several small-tournament matches were among Kalshi's busiest markets of the day. Golf was 17%, almost all of it on the winner market for the PGA Tour's VidantaWorld Mexico Open, about 7.5 million contracts.
• Polymarket is global. Soccer was 30% of its sports volume and esports 29%, with Counter-Strike and Dota 2 matches among its top ten markets overall. US football was under 7%.
• Baseball has gone quiet. With the World Series over, MLB was under 1% of sports volume on both.

That split matches the customer bases: Kalshi serves US residents, while Polymarket's international site is closed to them so its sports trading leans towards soccer and esports, which have bigger followings outside the US than American football does.

Trading is extremely concentrated

On both platforms the top 100 markets carried about half of all trading, and the top 1%, about 1,700 markets on Kalshi and 2,700 on Polymarket, carried 90–94%. Most listed markets exist for completeness: every match, every player, every price level. They make the menu look enormous, but on any given day only a few thousand of them matter, and those few thousand set the prices most traders actually see.

The busiest markets

24-hour volume by outcome, 30 October 2026.

Election week in the data

Five days before the vote, election markets were the busiest single markets on both platforms. On Kalshi, the Texas Senate race and the House and balance-of-power markets alone accounted for more than 12 million contracts in the 24 hours. On Polymarket, the three busiest outcomes of the House and Senate control markets took about $5.1 million, nearly 8% of all its trading. Expect politics' share to peak on election night and fall back sharply once the races are called. By mid-November, with the election settled, sports will almost certainly dominate both platforms again, and the NFL and NBA seasons will take a larger share than on this snapshot, which fell on a Thursday-to-Friday window with no NFL Sunday slate. A repeat of this study after the election would show how much of today's political trading is seasonal.

Open markets by category

Volume and listings are different things. Sports dominated listings on both platforms: 61% of Kalshi's open markets and 85% of Polymarket's. But on Polymarket, sports drew only 27% of the day's volume, while politics, with 6% of listings, drew 26%. Measured by the lifetime volume of markets still open, politics led on both platforms, at 49.5% on Kalshi and 61.7% on Polymarket, because long-running election markets have been trading for months.

What it means

• For traders: liquidity lives in a small number of markets. If you want tight prices, stick to the busiest ones; our spreads study shows how costs rise in quiet markets.
• For the regulatory fight: half of Kalshi's trading is sports, which is why sports contracts are at the centre of the state lawsuits and the CFTC's swap proposal (our report). Kalshi's own claim of more than $1 billion in non-sports revenue (our report) is its answer.
• For the midterms: election markets were the single busiest markets on both platforms five days before the vote. Our Election Day guide explains how they settle.

How our numbers compare with published volume figures

Kalshi and outside trackers publish monthly volume figures, such as the roughly $65 billion Kalshi was reported to have traded in October. Our count is not comparable with those. We counted only event contracts listed in Kalshi's public markets data, excluding combination markets and products such as perpetual futures, over a single day, and Kalshi's published figures may use different scope and counting conventions. Our purpose is the mix of trading, not the total.

Limitations

This is one 24-hour window, ending on a Friday afternoon (UTC) in the last week before the US midterms, so politics is likely higher than usual. Weekly sports schedules also move the mix: a different day would have more NFL or less tennis. Kalshi volume is in contracts and Polymarket's in dollars, so only shares are comparable. Categories are each platform's own labels grouped by us. Polymarket US and Kalshi's combination markets are not included.

Data

• Volume, listings and spreads by category (CSV)
• Spread statistics (CSV)

Related reading

• Bid-ask spreads on Kalshi and Polymarket
• Kalshi vs Polymarket prices: 351 outcomes compared
• Sports prediction markets explained
• Kalshi raises $1 billion at a $40 billion valuation
• Polymarket top traders: who makes money?

This study uses public market data and is not investment advice.