Kalshi Crushes Polymarket as $5.6B Prediction Market War Explodes

Key Points

• During the week ending May 18, Kalshi controlled 70.8% of total prediction market activity. The platform handled $3.99 billion in notional trades, while Polymarket slid 15% from the previous week to $1.65 billion, pushing the gap between both firms much wider.
• Sports trading, alongside Kalshi’s fast-growing “Exotics” contracts built around combo-style wagers, powered most of the exchange’s expansion. At the same time, Polymarket kept losing traction across crypto, political, and sports categories even as major global events continued drawing attention.
• Governments across Asia started tightening scrutiny around offshore prediction markets. India prepared new enforcement action, Indonesia moved to block Polymarket over gambling concerns, and South Korean authorities began examining whether the platform supports illegal betting operations.

For years, the market treated blockchain-based prediction platforms as untouchable leaders. That belief now faces pressure from a direction few expected. Kalshi, once viewed as the slower and more institutional exchange because of its CFTC oversight, has started widening the distance from Polymarket far faster than many analysts predicted only months earlier.

Trading volumes keep moving, transaction patterns are shifting, and sports-related activity is changing user behaviour across both platforms. Meanwhile, regulators throughout Asia have started reacting with stronger enforcement measures. Yet the real importance of this rivalry stretches beyond weekly billion-dollar figures. Prediction markets are no longer sitting inside a narrow political speculation corner. They are evolving into large event-driven trading systems that increasingly resemble modern betting infrastructure.

Kalshi’s Advantage Expanded Faster Than Analysts Expected

The gap separating the two biggest prediction market platforms grew rapidly during the week of May 18. Combined notional volume across Kalshi and Polymarket climbed to $5.64 billion. From that figure alone, Kalshi processed $3.99 billion and secured 70.8% of total activity after recording a 3% weekly increase.

Polymarket moved in the opposite direction. Its weekly volume fell 15%, sliding from $1.94 billion to $1.65 billion and giving Kalshi a much stronger lead across the sector. Only a few weeks ago, the rivalry appeared far tighter. During the week of March 30, Kalshi maintained about a three-to-two lead after recording $2.90 billion in volume against Polymarket’s $1.97 billion. Since that period, the distance between the two exchanges has expanded instead of closing.

Across roughly six weeks, Kalshi added close to $1.2 billion in weekly trading volume. Polymarket headed the other way and lost nearly $370 million during the same stretch. Those changes are starting to alter how analysts view the sector because the upper end of the market no longer looks as competitive as it did earlier this year.

Monthly Data Made the Gap Harder to Ignore

The wider separation became even clearer once monthly figures entered the picture. Across the first three tracked weeks of May, Kalshi produced nearly $12 billion in trading volume, placing the exchange within reach of the $14.81 billion monthly record it set in April.

Polymarket generated around $5.19 billion during the same period. That pace remained far below the level required to approach the platform’s March high of $10.57 billion. Three straight weeks near the $4 billion level also point toward something larger than a one-off event surge. Kalshi posted $4.13 billion during the week of May 4, dipped slightly to $3.88 billion in the following week, then recovered again to $3.99 billion by the week of May 18.

Polymarket, meanwhile, has failed to move above the $2 billion weekly notional trading threshold since the week ending April 13.

Transaction Activity Reshaped the Competition

Volume figures alone do not fully capture the changes unfolding between both exchanges. Back in the week of March 23, Polymarket processed far more transactions than Kalshi. The platform handled 26.3 million transactions, while Kalshi recorded 19 million. Six weeks later, the balance flipped completely.

By the week ending May 18, Kalshi processed 25.8 million transactions after posting a 7.3% weekly increase. Polymarket handled 17.4 million transactions and managed only a 0.9% rise during the same timeframe. That reversal matters because transaction activity often reflects how users interact with a platform over time. Higher transaction levels can signal stronger retention, wider participation, and more frequent trading behaviour across the exchange.

Kalshi’s taker volume also continued climbing higher. During the week of May 4, the figure reached $1.41 billion after rising 5.7% from the previous week’s $1.33 billion. Transaction totals during that period also increased 4.9% and reached 24.3 million.

Polymarket displayed a different trend altogether. Its global taker volume climbed 6.6% to $732 million during the same week despite weaker overall market volume. Several high-profile events settled at once, including UFC 328, Barcelona against Real Madrid, Bayern against PSG, along with multiple NBA playoff matchups.

Still, fee performance exposed a far weaker picture underneath those activity figures. Combined fees across Polymarket and Polymarket US dropped sharply from $8.46 million to $3.67 million within a single week.

Once Limitless, predict.fun, and Opinion entered the calculation, total fees across non-Kalshi platforms fell 59% to $3.97 million. That result marked the weakest weekly fee total recorded in the dataset. Analysts viewed the decline as a warning sign because stable activity levels no longer seemed to match equally strong trading quality.

Sports Trading Turned into Kalshi’s Strongest Advantage

Prediction markets are starting to behave more like dedicated sports trading ecosystems, and that shift currently favours Kalshi in a major way. During the week of May 18, the exchange generated roughly $1.59 billion in sports-related volume, while Polymarket recorded $675.5 million. Much of Kalshi’s strength came from its expanding “Exotics” category, which market participants widely associate with combo and parlay-style contracts.

That difference carries importance because parlay-style products often increase trading frequency, keep users active for longer sessions, and encourage higher spending patterns. Traditional sportsbooks have depended on the same structure for years since multi-event combinations usually attract more participation than isolated bets.

Between May 4 and May 10, Kalshi’s Exotics category jumped 23.2% from the previous week and reached $511.6 million in notional volume. Its share of combined sports and Exotics trading also climbed from 13.1% to 15%. NBA playoff action became one of the largest forces behind that surge in activity. Contracts linked to the Oklahoma City Thunder appeared in four of Kalshi’s top 20 weekly markets, while the exchange’s Pro Basketball Champion market carried the highest open interest across the platform.

Polymarket’s sports trading followed a different path during the same stretch.

Its sports-related volume fell 7.8% from the previous week even though major playoff games continued attracting attention. Instead of focusing heavily on individual matches and playoff series, Polymarket users showed stronger interest in international tournament markets such as the 2026 FIFA World Cup.

That contrast revealed a growing behavioural divide between the two platforms. Kalshi users increasingly concentrated on short-duration sports events that encouraged repeated trading activity. Polymarket users, meanwhile, appeared more drawn toward broader thematic speculation tied to macro-level events.

Crypto and Politics Continue Pulling the Market in Different Directions

Sports contracts still generate the biggest trading numbers, yet crypto and politics continue to define how both exchanges compete and attract users. During the May 4 to May 10 reporting window, crypto markets turned into a tighter battle than many expected. Kalshi moved ahead of Polymarket by a narrow margin and captured nearly 55% of total combined crypto trading volume.

Kalshi’s crypto notional volume rose 14.4% from the previous week, largely fuelled by Bitcoin prediction markets tied to short-term price levels and broader long-range contracts. Meanwhile, Polymarket recorded only a 2.1% increase in crypto activity. That gap drew attention because many traders once believed Polymarket’s blockchain-based design would secure a stronger hold over crypto-centred speculation.

Politics tells a very different story, and Polymarket still holds firm control there. The exchange commands 92.6% of the combined political notional volume across both platforms. Heavy trading continued around contracts linked to a possible US-Iran peace agreement, the 2028 presidential nominations, and the broader 2028 US election race.

Kalshi approached political trading from a more domestic angle. Activity stayed concentrated around the Los Angeles mayoral contest, the California governor race, and predictions tied to control of the US House during the 2026 midterm elections. Beneath those headline figures, analysts spotted another pattern taking shape. Open interest in Kalshi’s 2028 Democratic Nominee market remained high despite softer weekly trading, hinting that some participants may already be positioning for longer political bets rather than chasing only fast-moving speculation.

Polymarket US Produced a Very Different Trend

A more puzzling signal emerged from Polymarket’s American-facing business. During the week ending May 18, trading volume on Polymarket US climbed 7.5% and reached $447.7 million, despite weaker performance across the platform’s broader global operations.

Earlier numbers, however, showed almost the opposite trend. In the May 4 reporting period, Polymarket US taker volume plunged 78.9% from the previous week and fell from $125.6 million to only $26.5 million. Transaction activity dropped 73%, while fee generation slid 77.9%.

That decline surprised market watchers because it arrived during an active stretch of NBA and NHL playoff betting. Some analysts pointed to the smaller number of second-round NBA games as a possible reason for softer trading activity, yet the drop looked too deep to blame on scheduling alone. The sharp contrast between global activity and US-focused trading also exposed a larger issue, prediction market liquidity still appears divided across regions and different operating structures.

Asian Regulators Begin Increasing Pressure

As the rivalry between Kalshi and Polymarket grows stronger, regulators across Asia have started paying closer attention to the sector. India is expected to move toward formally blocking both exchanges while authorities tighten action against offshore operators that continue operating despite wider restrictions on online gaming. Officials are increasingly treating event-based contracts as prohibited money gaming products.

The decision could carry major weight because India remains one of the biggest online gaming markets anywhere in the world. Even limited enforcement measures may slow future user expansion for offshore prediction exchanges. Indonesia, meanwhile, has already moved further.

Indonesia’s Ministry of Communication and Digital Affairs, better known as Komdigi, blocked Polymarket after classifying the platform as an online gambling service that enables money-based betting on uncertain events. South Korea also opened a review into whether Polymarket carries content connected to illegal gambling activity.

The timing of these actions matters because prediction markets expanded quickly while regulators still treated crypto exchanges, sportsbooks, and online casinos as separate categories. Those boundaries now appear far less clear. Modern prediction platforms combine elements from all three industries, creating fresh uncertainty around regulation and legal classification.

Expert Review: Why the Kalshi and Polymarket Fight Reaches Beyond Prediction Trading?

The competition between Kalshi and Polymarket reflects a larger transition unfolding across speculative finance and digital wagering markets. Kalshi’s recent momentum suggests regulated platforms may now scale faster than crypto-native rivals once products start reaching wider audiences. Institutional confidence, stronger compliance structures, and easier user experiences appear to carry greater value as prediction trading moves beyond small political trading circles.

Polymarket still holds several structural strengths that remain difficult to ignore. Political speculation depends heavily on fast information cycles, social media momentum, and global narrative trading, areas where blockchain-based liquidity systems continue performing well. Across the wider betting and trading industry, another development has also started drawing attention, convergence.

Prediction markets no longer revolve only around elections or unusual headline events. Sports parlays, crypto speculation, economic forecasting, and entertainment contracts are steadily merging into one connected event-trading system. Platforms capable of handling regulatory pressure while also attracting mainstream participation may secure the strongest long-term advantage.

At the same time, the risks surrounding the sector are becoming more difficult to dismiss. Fragmented regulation could severely limit international expansion opportunities. Compliance expenses may continue rising, while platforms dependent on offshore users could face deeper exposure if more countries adopt measures similar to Indonesia’s crackdown.

For now, Kalshi’s advantage appears tied to momentum, sports-driven market demand, and stronger regulatory positioning inside the United States. Polymarket faces a different challenge in the months ahead, stabilising weaker trading volumes while defending its lead in political speculation and large global event markets. What happens next could shape the future of prediction trading itself. The industry may either grow into a mainstream financial entertainment sector or remain caught between gambling laws, securities oversight, and crypto enforcement battles that continue changing from one country to another.