- ▸ Kalshi volume plunged 49.5% WoW to $2.09B despite PGA Championship-driven activity, cutting its combined K+P share from 72.1% to 56.9%.
- ▸ Polymarket global held relatively steady (-1.7% WoW to $1.58B) as FIFA World Cup and European football markets supported activity.
- ▸ Polymarket US rebounded sharply, with taker volume up 123.4% WoW and transactions more than doubling.
Kalshi notional volume fell 49.5% week-over-week to $2.09B for the week beginning May 11, its sharpest single-week decline in the dataset, after hitting a record $4.13B the prior week. Polymarket global held comparatively steady, dipping just 1.7% to $1.58B, its most resilient week relative to Kalshi in over a month. Kalshi’s share of combined K+P notional fell from 72.1% to 56.9% in a single week.
The calendar explains most of it, with no UFC event, an NBA between-series lull, and a lighter domestic sports slate all hit Kalshi disproportionately given its sports-heavy mix. Polymarket’s floor held up because the FIFA World Cup continued to build and end-of-season European football provided sustained volume. Polymarket US reversed its prior-week collapse with taker volume up 123.4% and transactions more than doubling week-over-week.
Kalshi vs. Polymarket head-to-head
Kalshi vs. Polymarket 6-Week Comparison
| Week Start | Kalshi Volume | Polymarket Volume | Kalshi Transactions | Polymarket Transactions |
|---|---|---|---|---|
| 4/6/2026 | $3.54B | $2.48B | 22.2M | 22.3M |
| 4/13/2026 | $3.06B | $2.04B | 20.9M | 21.4M |
| 4/20/2026 | $3.91B | $1.96B | 23.8M | 19.2M |
| 4/27/2026 | $3.81B | $1.71B | 23.2M | 14.8M |
| 5/4/2026 | $4.13B | $1.60B | 24.3M | 15.8M |
| 5/11/2026 | $2.09B | $1.58B | 13.0M | 15.9M |
Kalshi’s drop snapped a five-week streak of gains and brought volume back to late-February levels. Polymarket global outpaced Kalshi on transactions (15,858,566 vs. 13,045,511) for the first time since early April, a reversal from the 24.3M vs. 15.8M gap just one week prior. The six-week trend still shows Kalshi growing its share structurally, but the week of May 11 is a clear reminder of how calendar-dependent that volume is.
Top platforms snapshot: Week of May 11
| Metric | Kalshi | Polymarket | Polymarket (US) | Total |
|---|---|---|---|---|
| Notional volume | $2.09B | $1.58B | $140.23M | $3.80B |
| Taker volume | $701.21M | $650.59M | $59.27M | $1.41B |
| Transactions | 13.05M | 15.86M | 672.05K | 29.58M |
| Fees | $17.85M | $6.83M | $1.03M | $25.71M |
Kalshi notional fell 49.5% and taker volume dropped 50.2% to $701M, both moving in lockstep, pointing to a volume-driven decline rather than a mix shift. Transactions fell 46.4% to 13,045,511.
Polymarket global held fairly steady across metrics for the week. Notional volume was down just 1.7%, taker volume was down 11.1% to $651M, and transactions essentially flat at +0.3%. Fees of $6.83M were up 4.9%, the only major platform to post a fee increase. The taker volume gap between the two platforms narrowed from $677M the prior week to just $50M. Note: Polymarket’s category breakdown total ($1.37B) is lower than reported notional ($1.58B), likely reflecting volume in unmapped categories not captured in the Dune data breakdown.
Polymarket (US) reversed sharply after last week’s collapse. Its notional volume climbed 91.6% to $140.2M, with taker volume up 123.4% to $59.3M, and transactions up 106% to 672,054. More on this below.
On fees: Kalshi’s $17.85M on $2.09B of notional implies a significantly higher fee rate than Polymarket’s $6.83M on $1.58B. For a full breakdown of prediction market fee structures, see our fees tracker.
Kalshi and Polymarket category breakdown: Week of May 11
Core sports on Kalshi fell 50.3% while Exotics dropped even harder at 63.8%, compressing Exotics’ share of the combined sports bucket from 15.0% to 11.4%. The NBA finals second round had gaps between series games and there was no key UFC event to anchor volume as UFC 328 did the previous week.
According to our internal prediction market volume tracking, Kalshi’s Pro Basketball Champion market remained No. 1 but fell from $8.4M to $6.0M in weekly volume, with open interest dropping from $76.5M to $45.9M. Colorado Avalanche replaced Carolina Hurricanes as the Stanley Cup favorite, and an NBA Finals Matchup market (OKC vs. NY) entered the top 20.
The IPL Champion market at No. 13 is worth a note as well. International cricket breaking into Kalshi’s top 20 signals a broadening scope beyond domestic sports. Polymarket sports fell just 7.9%, with the FIFA World Cup surging 74% to $84.3M and heavy end-of-season European football volume providing a floor. The PGA Championship was another notable market this week, driving $333.5 million in notional volume at Kalshi. Polymarket’s comparable market showed nearly $9.0 million in volume, highlighting once again the sports gap on major US-based sporting events.
Kalshi category breakdown
Kalshi Category Breakdown: Week of May11
Polymarket category breakdown
Polymarket Category Breakdown: Week of May 11
Kalshi politics fell 45.2% to $20.4M but climbed the rankings relatively. The platform had some political markets crack the top 20 for the past week, including LA mayor race at No. 2, KY-04 Republican primary at No. 3, and a “What will Trump say this week?” market at No. 17. On Polymarket, Politics fell 29.0% while the Trump category dropped a steeper 44.8%, partly due to the US-Iran peace deal resolving after generating $26.7M the prior week.
Crypto was down on both platforms: Kalshi -35.7% to $249.6M, Polymarket -10.9% to $279.8M. After Kalshi recently took over the lead in crypto volume, Polymarket is back up top, albeit marginally. Four separate daily Bitcoin price markets on Polymarket drove notable volume across the week.
Another key move during the week of May 11 came from the culture and entertainment category. Culture on Polymarket surged 151.3% to $66.6M, driven by Eurovision Winner 2026 closing (Finland led at 47%) and the Elon Musk tweet count market ($6.6M). On Kalshi, Entertainment was the only category to grow, up 44.3% to $13.3M, driven primarily by the Survivor Season 50 market.
Note: DeFi Rate’s top category data is based on USD-at-price volume, or actual dollars traded, rather than notional volume, which values each contract at $1 regardless of trading price.
Polymarket US rebound
After collapsing 79% on taker volume the prior week, Polymarket US rebounded hard. The top 20 was all sports, with 18 of 20 markets already closed. NBA second round dominated (Detroit vs. Cleveland, OKC vs. Lakers), followed by MLB game markets, Italian Open tennis (Sinner vs. Medvedev), the PGA Championship, and esports breaking in for the first time with Counter-Strike IEM Atlanta and LoL LPL both in the top 20.
The breadth of the slate drove the rebound. Going into the NBA Finals in June, the question is whether the US product can sustain this activity level or whether it remains highly event-dependent.
What to watch
The week of May 11 was a sort of test for Kalshi volume without a major sports driver, and volume dropped nearly in half, despite NBA playoffs continuing and the PGA championship playing out. The NBA Finals and FIFA World Cup in June are the next major catalysts, with the NBA semi-finals tipping off this week.
Through two full weeks, Kalshi is averaging $3.11B/week in May against April’s $3.70B/week pace that produced a record $14.81B monthly total. Matching that will require a meaningful back-half rebound. The NBA Finals, upcoming French Open, World Cup lead-up and key 2026 primaries could help push the platform, but it likely won’t be enough to surpass last month’s record. Polymarket is further off pace at $1.59B/week against April’s $2.25B/week, and at current trajectory is unlikely to match last month’s $9.01B without a significant catalyst. How both platforms respond to the June sports calendar including NBA Finals, FIFA World Cup and Stanley Cup will set the tone for what has been a steadily widening volume gap since March.
