Prediction Markets Hit Record $28.4 Billion in Monthly Volume in May

Prediction markets reached a new monthly volume record of $28.4 billion in May according to data from Artemis. This number tops the previous high of $27.1 billion set in January this year and marks four consecutive months with higher volumes.

The streak itself says more than the headline number does. January’s spike fed off election-cycle leftovers and new year positioning. May, on the other hand, did not really have any equivalent catalyst and still beat it. This seems to suggest that activity on prediction market platforms are shifting from sudden spikes based on events toward a steady floor. The idea of these markets being a venue for occasional curiosity is gradually moving to an always-on space.

Kalshi recorded $17.3 billion in volume last month. This is a monthly record in itself for the platform and a 29% increase in volume over the previous month. What’s more noteworthy is the fact that about 61% of all volume came from Kalshi and it processed nearly twice the volume of Polymarket, which saw $8.4 billion. Taken together, however, the duopoly is still there as both these platforms made up close to 90% of the trading volume in May.

If we go back to a year ago, this split between the two largest platforms would have read backwards. Polymarket built the category and held market dominance all the way from 2024 up until September 2025, when Kalshi tipped the scales. We tracked the same reversal inside crypto-themed contracts earlier this month, where Kalshi’s share went vertical from February on.

The reason for this flip is actually quite comprehensible. Kalshi’s regulated US status has helped drive its sports business, which carries most of its volume. Conversely, Polymarket was mired in a host of regulatory obstacles through large parts of the last quarter. This is not to say that Polymarket’s volumes have fallen off a cliff month on month but that it just stopped climbing.

Why Four Straight Months Beats One Record

A single record can be a fluke. A sports calendar, a viral market, one big election can all spike a month and then fade. Four months in a row is harder to wave off. It means the floor under the sector keeps rising even when the catalyst rotates out.

That baseline is the maturation signal. Prediction markets are no longer waiting for an election to matter. Newsrooms cite the odds, hedge funds watch them, and market makers like Wintermute now quote two-sided prices across the largest venues. The plumbing is starting to look like a real derivatives market rather than a betting novelty.

Regulation and Builders Are the Next Leg Up

Kalshi’s lead lines up with the regulatory wind. The CFTC has signaled clearer prediction-market guidance is coming, which favors the licensed exchange. Polymarket is playing the same game from the other end, having bought a CFTC-licensed venue to re-enter the US market it was largely locked out of.

The builder layer is the wild card. Hyperliquid switched on its HIP-4 outcome contracts on mainnet on May 2, letting developers deploy their own markets on top of an exchange that already clears hundreds of billions in monthly volume. The early take is tiny, around $87.7 million, well under 1% of the sector. But it hints at the next phase: markets anyone can launch, settled on-chain, riding a base of 1.4 million existing traders.

For now the shape is simple. Two big venues, one of them regulated and pulling away, sitting on a sector that just posted its strongest month with nothing forcing it higher.