- ▸ Kalshi posted $17.91B in notional volume in May, a ninth consecutive monthly record while Polymarket fell to $7.08B, its lowest since January.
- ▸ Kalshi processed 111 million transactions in May vs. Polymarket’s 69 million, the widest transaction gap in the tracked period and a reversal of the Polymarket lead that held through March.
- ▸ The week of June 1 brought a critical World Cup signal: Polymarket US doubled to $882M in weekly notional, its largest weekly total on record, with 14 of its top 20 markets by trading volume tied to the tournament.
Kalshi closed May with $17.91 billion in notional volume, its ninth consecutive monthly record and a 21% jump from April’s then-record $14.81B, according to DeFi Rate’s prediction markets volume tracker. Polymarket posted $7.08 billion in the same month, representing a 21% decline from its $10.57B March peak and its lowest monthly total since January. The two platforms were heading in opposite directions going into June, which will see the start of quite possibly the largest sports betting catalyst to date with the 2026 World Cup kicking off.
Apart from notional volume, a transaction gap is also forming between the top two prediction market platforms. Kalshi processed 111 million transactions in May, up from 94 million in April. Polymarket processed 69 million, down from 87 million, giving Kalshi a 61% transaction advantage, the widest margin since DeFi Rate began tracking both platforms. That lead first opened in April, when Kalshi’s count eclipsed Polymarket’s for the first time.
Kalshi vs. Polymarket Monthly Volume and Transactions
Two Kalshi combo contracts, parlay-style multi-leg sports markets on the NBA finals, landed in the platform’s top 20 markets by trading volume over the last seven days, another signal for where prediction market activity is concentrating. Sports and Exotics together accounted for 84% of Kalshi’s weekly notional during the week of May 25 and 85% during the week of June 1. The latest volume data reiterates the importance of sports markets including parlays in the overall prediction market ecosystem.
May volume highlights: Sports, parlays and a widening platform split
Kalshi’s May volume mix was heavily concentrated in sports yet again. During the week of May 25, Sports accounted for $2.38B and Exotics, Kalshi’s parlay-style combo contracts, added $1.17B, together representing 84% of Kalshi’s weekly notional volume, according to tracking from Dune analytics. Crypto contributed $527M. Everything else, including Elections at $44.6M, Politics at $9M, and Economics at $11.6M, was marginal by comparison.
Exotics first crossed $1B in weekly notional volume in the week of April 20. The category now regularly surpasses that threshold, trending up especially during key events like the NBA Finals. Kalshi’s Exotics growth has been one of the more consistent volume trends of 2026, and the appearance of two combo contracts in the top 20 markets by trading volume last week, alongside the NBA Finals champion and LA mayoral race, reflects how mainstream the product has become on the platform.
Polymarket’s May mix looked different. During the week of May 25, Sports led at $952M but Politics ($242M), Trump markets ($99M), and Crypto ($297M) each carried real weight. The more balanced distribution across categories, with meaningful politics and crypto exposure, remains the clearest structural differentiator between the two platforms. Polymarket trades differently than Kalshi, and May’s data makes that contrast as clear as ever.
Week of June 1: Kalshi climbs, Polymarket US breaks out
Kalshi notional volume rose 6.1% to $4.46B in the week of June 1, its highest weekly total since May 4. Exotics climbed to a new tracked high of $1.32B (+13% week over week) driven by the first two games of the NBA Finals. Elections surged to $115.8M from $44.6M the prior week, a 160% increase driven by California governor primary and LA mayoral markets. Crypto on Kalshi reached $713M, up from $527M.
On Polymarket Global, the story was Crypto with Bitcoin’s recent sell-off and price action a main catalyst. The category more than doubled from $297M to $664M week over week, lifting total Polymarket notional volume 14.4% to $1.91B. Politics remained significant at $169M, with Trump markets adding $46M on top.
The Polymarket US number was the standout of the week. The US platform posted $882M in notional volume, more than double its $439M the prior week and the largest weekly US total in recent tracked data. Fourteen of Polymarket US’s top 20 markets by trading volume over the last seven days were World Cup contracts, and the tournament hadn’t even kicked off yet. The Mexico vs. South Africa opener on June 11 and the US vs. Paraguay match on June 12 were both closing soon as of this writing, with $1.9M and $902K in trading volume respectively.
Exchange fees moved in different directions. Kalshi’s weekly fees fell 11.7% to $33.51M despite higher notional volume, a signal of mix shift toward lower-margin contracts. Polymarket US fees rose 26% to $4.34M on the doubled volume.
Polymarket Global fees rose marginally from $6.56M to $6.69M, a 2% WoW increase. Along with the platform’s 14.4% notional volume gain, the smaller fee percentage increase reflects a lower average fee rate on the crypto-heavy mix driving much of the weekly volume growth. Total fees across tracked platforms came to $46.06M for the week of June 1, down from $50.17M the prior week.
Top markets: NBA Finals, California primaries, and a World Cup takeover
Kalshi’s top 20 markets over the last seven days, by USD-at-trading-price volume, were led by the NBA championship winner market ($17.7M, Knicks 78%), LA Mayoral Election winner ($17.2M, Karen Bass 59%), and 2026 Men’s World Cup winner ($7.7M, France 16%). The NBA Finals series contract and two combo parlays also made the list, alongside California governor and LA mayoral primary markets that generated a cluster of political volume ahead of June 2 primaries. The Fed’s June decision market placed fifth at $3.6M, with the market pricing a 99% chance of no change.
Kalshi Top 10 Markets: Last 7 days (USD at trading price)
| # | Market | Volume | Leading |
|---|---|---|---|
| 1 | Pro Basketball Champion | $17.7M | Knicks 78% |
| 2 | Los Angeles Mayoral Election Winner | $17.2M | Karen Bass 59% |
| 3 | 2026 Men’s World Cup Winner | $7.7M | France 16% |
| 4 | Game 3: San Antonio at New York | $6.2M | Knicks 55% |
| 5 | Fed Decision in Jun 2026 | $3.6M | Maintain rate 99% |
| 6 | Los Angeles Mayor Matchup | $3.4M | Raman vs. Bass 99% |
| 7 | Series Exact Score: NY (3) vs SA (2) | $2.8M | NY 4–0 33% |
| 8 | LA Mayoral Election: Spencer Pratt Vote % | $2.6M | 20%+ 100% |
| 9 | CA Governor Primary: Who Will Advance | $2.3M | Steve Hilton 95% |
| 10 | Combo: NY Knicks win, Under 231.5 | $2.3M | NY, Under 231.5 50% |
Polymarket’s top markets reflected a more global, current-events-driven audience. World Cup Winner led at $287.8M with $18.1M in open interest, by far the largest single market on either platform. Fed Decision in June ranked second at $19.1M with $6.3M in OI. The US-Iran peace deal ($14.4M), Democratic Presidential Nominee 2028 ($12.4M, Newsom 25%), and Presidential Election Winner 2028 ($9.8M, JD Vance 16% with $37.7M in open interest) rounded out the top five. Politics dominated the mid-list, with the Seoul mayoral election, California governor, French presidential election, and multiple Iran-related markets all appearing in the top 20.
Polymarket Global Top 10 Markets: Last 7 days (USD at trading price)
| # | Market | Volume | Leading |
|---|---|---|---|
| 1 | World Cup Winner | $287.8M | France 16% |
| 2 | Fed Decision in June | $19.1M | No change 99% |
| 3 | US x Iran Permanent Peace Deal | $14.4M | Dec 31, 2026 68% |
| 4 | Democratic Presidential Nominee 2028 | $12.4M | Newsom 25% |
| 5 | Israel Announces Lebanon Ceasefire Extension | $11.3M | Closed |
| 6 | Presidential Election Winner 2028 | $9.8M | JD Vance 16% |
| 7 | What Price Will Bitcoin Hit in May | $9.7M | Closed |
| 8 | 2026 NBA Champion | $8.8M | Knicks 78% |
| 9 | Strait of Hormuz Traffic Returns by End of May | $8.0M | Closed |
| 10 | What Price Will Bitcoin Hit in June | $7.7M | $65,000 81% |
Polymarket US was almost entirely World Cup. Nine of the top ten markets by trading volume were soccer contracts: Portugal winner ($2.1M), Mexico vs. South Africa ($1.9M), Spain winner ($1.1M), Mexico winner ($991K), France winner ($873K), and multiple group-stage winner markets. The NBA champion market for New York placed sixth at $942K, the only non-soccer contract in the top ten.
Polymarket US Top 10 Markets: Last 7 days (USD at trading price)
| # | Market | Volume | Leading |
|---|---|---|---|
| 1 | FIFA World Cup Winner: Portugal | $2.1M | Portugal 11% |
| 2 | Mexico vs. South Africa (Jun 11) | $1.9M | Mexico 70% |
| 3 | FIFA World Cup Winner: Spain | $1.1M | Spain 17% |
| 4 | Memorial Tournament Winner: JT Poston | $1.0M | Closed |
| 5 | FIFA World Cup Winner: Mexico | $991K | Mexico 2% |
| 6 | 2026 NBA Champion: New York | $942K | NY 78% |
| 7 | US vs. Paraguay (Jun 12) | $902K | USA 50% |
| 8 | FIFA World Cup Winner: France | $873K | France 16% |
| 9 | FIFA World Cup Group G Winner: Belgium | $852K | Belgium 68% |
| 10 | Australia vs. United States (Jun 19) | $845K | Australia 21% |
What to watch in June
Kalshi’s $4.46B in the week of June 1 puts it on pace for another monthly record, though sustaining that level through a full month is a different challenge than a single strong week. The NBA Finals (Knicks leading San Antonio 3-0 entering Game 4) and the Stanley Cup playoffs give sports markets sustained fuel through mid-month with World Cup group-stage play continuing for most of June. The Fed’s June 16-17 meeting is the primary macro catalyst outside sports.
The bigger question for June is whether the marquee event delivers on DeFi Rate’s $2.5B World Cup volume forecast across the tournament. Polymarket US’s pre-tournament surge, doubling to $882M before a match was played, with 14 of its top 20 markets already tied to soccer, suggests the ceiling may be higher if per-match engagement holds through the group stage and into the knockouts. The US opens against Paraguay on June 12, which ranked seventh on Polymarket US by trading volume last week at $902K. US currently leads in odds at 50% compared to 24% for Paraguay and 29% for a draw (tie).
