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Prediction markets just had their biggest month ever. Trading volume hit $29.4 billion in May, driven by a wave of retail brokers, institutional desks, and even sportsbook operators all scrambling to get a piece of the action.
Kalshi alone accounted for $17.3 billion of that total. That’s a staggering share — more than half the entire market — and it didn’t happen by accident. The platform has been signing broker partnerships at a fast clip, pulling in retail flow from platforms that previously had nothing to do with event-driven contracts. Polymarket, the other big name here, posted $8.4 billion in May volume, with around $1.5 billion of that coming from World Cup winner contracts. That’s not a niche product anymore. That’s a real market.
Moomoo Joins Robinhood and Interactive Brokers on Kalshi
Moomoo, the retail broker, recently teamed up with Kalshi to bring prediction market contracts to its users. The deal puts Moomoo alongside Robinhood and Interactive Brokers, both of which had already made similar moves. Clients on these platforms can now trade contracts tied to economic data releases, Federal Reserve decisions, and elections — all sitting right next to their regular stock and ETF positions. Pretty much a full menu now.
And it’s not just about adding a shiny new product. Brokers are clearly betting that event-driven contracts pull in a different kind of trader — someone who wants to take a view on a Fed rate decision without buying a bond or an options spread. Whether that customer sticks around is unclear yet, but the broker interest is real and it’s accelerating.
Wintermute and Galaxy Digital Move In From Different Angles
On the institutional side, Wintermute and Galaxy Digital are both active — but doing very different things. Wintermute has been expanding its liquidity provisioning on Kalshi and Polymarket, basically making it easier for retail and mid-size traders to get in and out of contracts without terrible fills. That’s the public-market play.
Galaxy Digital went a different direction. The firm launched an OTC swap business specifically for prediction markets, and it’s already handling large trades — a $10 million contract tied to U.S. crypto legislation was one example. Off-exchange, bespoke, structured around specific client needs. That’s a different clientele entirely. So you’ve got one firm tightening up the public order books and another building private channels for the big stuff. Both approaches are probably necessary as the market scales.
The $10 million crypto legislation trade is worth sitting with for a second. That’s not a speculative punt by a retail punter — that’s a firm or fund taking a real position on a policy outcome. It’s hedging, or something close to it. And that changes what prediction markets are, functionally. They’re not just novelty anymore.
Sportsbooks Starting to Feel the Heat
Polymarket’s World Cup volume is making traditional sportsbooks nervous. Flutter has been broadening its betting options and promotions in response. DraftKings and FanDuel are also digging deeper into prediction markets — though exactly how far they’re going, the source didn’t fully specify.
Polymarket’s combination contracts are part of what’s drawing traders in. More flexibility, more ways to structure a bet or a hedge, more reasons to stay on the platform rather than walking over to a sportsbook. Traditional operators are responding with expanded in-play markets and micro-betting options, trying to hold their ground during the periods when customer acquisition matters most.
It’s a real competitive fight now. Prediction markets were a curiosity two or three years ago. Now they’re generating the kind of volume that makes sportsbook executives pay attention.
One concrete example from the source: a New York bar used Kalshi contracts to offset the cost of running a promotion. That’s a small business using a financial instrument to hedge a marketing expense. That’s not something anyone predicted when these platforms launched.
Liquidity infrastructure is getting more serious across the board. Market makers are putting more capital to work on public venues. OTC desks are building out. Brokers are integrating. The whole ecosystem is getting denser and more interconnected, which tends to make markets stickier and harder to dislodge once they’re embedded.
Kalshi’s $17.3 billion in May volume.
Frequently Asked Questions
What was the total prediction market trading volume in May?
Prediction markets hit a record $29.4 billion in trading volume in May, with Kalshi accounting for $17.3 billion and Polymarket handling $8.4 billion of that total.
Which brokers are now offering Kalshi prediction market contracts?
Moomoo, Robinhood, and Interactive Brokers have all partnered with Kalshi to offer prediction market contracts to their retail clients.
