- ▸ Kalshi notional volume dipped 6.6% to $3.86B despite a 46% transaction drop signaling fewer, bigger trades.
- ▸ Kalshi is on pace to top April’s record $14.81B monthly total while Polymarket will likely fall short of its April volume.
- ▸ Polymarket US rebounded 84% WoW on a broad sports slate for the week.
Kalshi notional volume dipped 6.6% week-over-week to $3.86B for the week beginning May 11, a much softer decline than the transaction count suggests. Trades fell 46.4% to 13.0M, pointing to larger average trade sizes rather than a broad pullback in activity. Polymarket global held steady at $1.58B (-1.7%), while Polymarket (US) reversed its prior-week collapse with notional volume up 84.3% to $416.5M.
Kalshi maintained a 71.0% share of combined K+P notional, essentially flat from 72.1% the prior week. Unlike the transaction count, notional volume stayed strong, suggesting the activity that remained was concentrated in larger positions. The PGA Championship helped make up for fewer NBA playoff games and the absence of a major UFC event.
Kalshi vs. Polymarket trends
Kalshi vs. Polymarket 6-Week Comparison
| Week | Kalshi Volume | Polymarket Volume | Kalshi Tx | Polymarket Tx |
|---|---|---|---|---|
| 4/6/2026 | $3.54B | $2.48B | 22,157,345 | 22,349,643 |
| 4/13/2026 | $3.06B | $2.04B | 20,874,039 | 21,429,287 |
| 4/20/2026 | $3.91B | $1.96B | 23,788,403 | 19,220,738 |
| 4/27/2026 | $3.81B | $1.71B | 23,200,472 | 14,837,848 |
| 5/4/2026 | $4.13B | $1.60B | 24,327,253 | 15,805,153 |
| 5/11/2026 | $3.86B | $1.58B | 13,045,511 | 15,858,566 |
Head-to-head snapshot, Week of May 11
Kalshi notional volume dipped slightly from its peak weekly volume in the previous week, but the bigger story was the transactions divergence. Kalshi notional held up (-6.6%) despite the massive transactions drop, implying the average trade size grew substantially.
Polymarket global was essentially flat with taker volume down 11.1% to $651M and transactions up 0.3% to 15,858,566 (outpacing Kalshi for the first time since early April). 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, according to Dune data tracking.
| Metric | Kalshi | Polymarket | Polymarket (US) | Total |
|---|---|---|---|---|
| Notional volume | $3.86B | $1.58B | $416.53M | $5.86B |
| 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 |
Polymarket (US) bounced back sharply, with notional volume up 84.3% to $416.5M, taker volume up 123.4% to $59.3M, and transactions up 106% to 672,054. A full NBA second-round slate, active MLB markets, PGA Championship, and Italian Open tennis all drove the rebound.
Regarding fees, Kalshi’s $17.85M on $3.86B of notional volume highlights a significantly higher fee rate than Polymarket’s $6.83M on $1.58B, a structural difference in how the two platforms monetize volume. For a full breakdown see our fees tracker.
What’s driving volume
Top market volumes below are from our DeFi Rate tracker and reflect USD-at-price (actual dollars traded), not notional volume.
Top volume drivers for the week at Kalshi
Sports continue to anchor the top of the board, led by the NBA playoffs. The Pro Basketball Champion market held at No. 1 as the conference finals matchups took shape. Colorado Avalanche emerged as the new Stanley Cup favorite, displacing Carolina Hurricanes, and an NBA Finals matchup market (OKC vs. NY) entered the top 20. The PGA Championship was another notable market last week, driving $365.2 million in overall volume at Kalshi, including $9.8 million in combos (parlays). Polymarket’s comparable market showed nearly $9.0 million in volume, highlighting once again the sports gap on major US-based sporting events. Meanwhile, there was no major UFC fight last week after the UFC 328 event the week before drove $51.8 million in notional volume.
Kalshi had some political markets crack the top 20, 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. Key primaries and 2026 midterm markets will continue to gain momentum leading up to November elections. A couple other notable drivers come from cricket and SpaceX. The IPL Champion market at No. 13 is notable, as international cricket gains in popularity among traders. And the SpaceX IPO timing market ranking No. 20 in volume the past week is a rare feat for the Companies category. the Survivor Season 50 market also continued to hold strong in the culture slot.
Top volume drivers at Polymarket for week of May 11
The FIFA World Cup winner market remained dominant at No. 1 by a wide margin, with France still leading at 18%. The end-of-season European football slate drove a heavy volume of closed markets across the top 20. The “Will Trump visit China by?” market closed in the top 3 after generating significant volume. The Eurovision Winner 2026 was a notable culture market, as was the Elon Musk tweet count market at No. 7.
The 2026 NBA Championship market sat at No. 8 with OKC leading in odds, consistent with Kalshi’s pricing. On the politics side, the 2028 Democratic Nominee ($7.2M, Newsom leading at 24%) was the top active market, with both 2028 presidential nomination markets and the 2028 general election maintaining steady open interest.
Polymarket US still mostly sports
Polymarket US’s volume is still almost entirely game-level sports, with 18 of 20 top markets closed by week’s end. The NBA second round dominated as Detroit-Cleveland and OKC-Lakers series and individual game markets anchored the top 10. MLB appeared in force with six game-level markets across the top 20, Italian Open tennis contributed two Sinner markets, and the PGA Championship landed at No. 5. Esports made the list for the first time, with Counter-Strike IEM Atlanta and LoL LPL both in the top 20, a new category worth watching as the US platform continues to broaden its mix within and outside of sports.
What to watch
Through two weeks, Kalshi is averaging $3.99B/week in May against April’s $3.70B/week pace that produced a record $14.81B monthly total, putting it on pace to exceed last month if the back half holds. Polymarket is averaging $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.
The NBA Finals starting in June and the FIFA World Cup will be markets to watch in June. It will also show us if Polymarket’s international sports appeal can help it close the gap somewhat on Kalshi on the back of World Cup trading. That volume divergence, building since March, is increasingly visible in the absence of major geopolitical or political events.
