Kalshi posted its highest single-week notional volume on record during the week ending May 4, tallying $4.13 billion, up 8.5% from $3.81 billion the prior week. Polymarket fell 6.2% WoW to $1.60 billion, its lightest week since late March. Kalshi now holds 72.1% of combined notional volume between the two platforms, up from 69.0% the week prior and from near parity in late February and early March.
As recently as the week of March 23, Polymarket was processing significantly more transactions than Kalshi (26.3M vs. 19.0M), but that has fully reversed.
Kalshi vs. Polymarket (Last Six Weeks)
| Week | Kalshi Volume | Polymarket Volume | Kalshi Tx | Polymarket Tx |
|---|---|---|---|---|
| Mar 30 | $2.90B | $1.97B | 20.10M | 22.70M |
| Apr 6 | $3.54B | $2.48B | 22.20M | 22.30M |
| Apr 13 | $3.06B | $2.04B | 20.90M | 21.40M |
| Apr 20 | $3.91B | $1.96B | 23.80M | 19.20M |
| Apr 27 | $3.81B | $1.71B | 23.20M | 14.80M |
| May 4 | $4.13B | $1.60B | 24.30M | 15.80M |
Kalshi vs. Polymarket head to head: Week of May 4
Kalshi’s notional volume lead over Polymarket has widened steadily since the start of April. Kalshi held a roughly 3-to-2 advantage with $2.90B vs. $1.97B the week of March 30. That has since stretched to more than 2.5-to-1 at $4.13B vs. $1.60B. The divergence accelerated sharply in April. While Kalshi added roughly $1.2B in weekly volume over the six-week window, Polymarket shed about $370M. The transactions shift is even more stark. From the week of March 23 to May 4, Polymarket and Kalshi flip-flopped positions, with Kalshi at 24.3M to Polymarket’s 15.8M for a swing of roughly 17 million transactions in six weeks.
This is a continuation of a trend we first flagged in the March volume report and that accelerated through Kalshi’s April record $14.81B monthly total. What’s changed in recent weeks is Polymarket’s decline spanning all major categories. It’s no longer just crypto and politics volume softening, but sports volume pulling back too, down from $786M the week of April 27 to $725M the week of May 4, even with the NBA playoffs in full swing. Kalshi’s sports-first model, reinforced by the growing Exotics (combos/parlays) product, is helping drive Kalshi’s lead in both overall volume and transactions.
Top platforms snapshot
A weekly snapshot of the two top prediction markets platforms plus Polymarket US clearly shows the US-facing exchange’s infancy. Polymarket US is still not near the scale of the other two, but weekly fees are becoming a significant revenue driver.
| Metric | Kalshi | Polymarket | Polymarket (US) | Total |
|---|---|---|---|---|
| Notional volume | $4.13B | $1.60B | $73.2M | $5.80B |
| Taker volume | $1.41B | $732M | $26.5M | $2.17B |
| Transactions | 24.3M | 15.8M | 326K | 40.4M |
| Fees | N/A | $3.15M | $517K | $3.67M |
Kalshi taker volume of $1.41B was up 5.7% week-over-week from $1.33B, according to Dune data, consistent with the notional volume gain. Transaction count grew 4.9% to 24.3M, continuing a steady climb that has added roughly 4 million weekly transactions since March 30.
Despite its continued four-week volume slide, Polymarket global taker volume of $732M was up 6.6% from $686M the prior week. That uptick is partly a function of market settlement with a high volume of large markets closing in the same week (UFC 328, Barcelona-Real Madrid, Bayern-PSG, several NBA first-round games). Transactions also rose 6.8% to 15.8M from 14.8M. Fees of $3.15M were down 48.5% from $6.12M the prior week, a much steeper drop than the 6.6% taker volume gain would imply. The likely explanation is that the markets resolving this week were lower-stakes, lower-fee events compared to what settled the week prior, rather than a slowdown in new trading activity. Polymarket recently rolled out a platform-wide fee expansion on March 30.
Polymarket US was the week’s clear soft spot and worth watching separately. Taker volume collapsed 78.9% week-over-week from $125.6M to $26.5M, transactions fell 73% from 1.2M to 326K, and fees dropped 77.9% from $2.34M to $517K. The meaningful drop across every metric simultaneously is surprising considering the NBA and NHL playoffs are in full swing. It could be in part a result of fewer NBA games in Round 2 of the playoffs compared to Round 1. Whether it also reflects a structural pullback or something else isn’t fully clear from the data alone, but the magnitude of the move in a single week is notable and worth tracking in the coming weeks.
On fees broadly: combined Polymarket + Poly (US) fees of $3.67M were down from $8.46M the prior week. Including Limitless, predict.fun, and Opinion, total non-Kalshi platform fees came to $3.97M, down 59% from $9.69M and the lowest weekly fee total in the dataset. Limitless dropped 79.6% to $228K despite growing notional volume, which suggests possible fee rate compression, inflated trading volumes, or something else going on structurally.
Kalshi vs. Polymarket category breakdown May 4-10
Kalshi continues to dominate on sports, but things get more interesting across other top categories. Notably, Kalshi has surpassed Polymarket on crypto market volume, perhaps surprising considering Polymarket’s blockchain-based structure. Also noteworthy is Polymarket’s massive lead on the Politics (including Trump) category (92.6% share) and significant 3-1 share lead in the smaller categories of Entertainment/Culture and Economics.
Kalshi vs. Polymarket Category Comparison: Week of May 4
Notes: Notional volume from Dune Analytics. Exotics rolled into Sports for Kalshi totals; Trump markets rolled into Politics for Polymarket totals. Cross-platform share calculated for Kalshi + Polymarket combined.
Polymarket vs. Kalshi market share on top categories
| Category | Kalshi | Polymarket | Combined | Kalshi Share |
|---|---|---|---|---|
| Sports (incl. Exotics) | $3.41B | $725M | $4.14B | 82.4% |
| Crypto | $388M | $314M | $702M | 55.3% |
| Politics (incl. Trump) | $37M | $464M | $501M | 7.4% |
| Culture / Entertainment | $9.2M | $26.5M | $35.7M | 25.8% |
| Economics | $7.0M | $21.7M | $28.7M | 24.4% |
Sports: Kalshi’s core sports notional grew 5.7% week-over-week and, combined with Exotics, held 82.4% of cross-platform sports volume. The NBA playoffs were the dominant driver. OKC Thunder markets appeared across four of Kalshi’s top 20 by weekly volume, according to our prediction markets volume tracker, led by the Pro Basketball Champion market, which carried the highest open interest on the Kalshi board by a wide margin.
Polymarket’s sports volume fell 7.8% week-over-week despite the playoffs, and its top sports market was the 2026 FIFA World Cup, which dwarfed anything on the Kalshi sports slate. The contrast reflects how differently the two platforms’ user bases engage with sports, Kalshi leading at the game and series level and Polymarket volume concentrating at the international tournament level.
Exotics: The combo/parlay product was the standout growth story at Kalshi, up 23.2% week-over-week to $511.6M in notional volume, lifting its share of the combined sports + Exotics bucket to 15.0% from 13.1% the prior week. We’ve been tracking this as a structural driver for several weeks now, and the trajectory is holding. Expect it to grow significantly once NFL starts back up in the fall.
Crypto: The most competitive category between the platforms at 55/45 in Kalshi’s favor is Crypto. Kalshi’s crypto notional volume rose 14.4% week-over-week while Polymarket’s edged up just 2.1%. Kalshi’s crypto markets are primarily driven by Bitcoin markets, both daily and longer-term price target markets, but they are gaining in popularity.
Politics: Polymarket continues to dominate Kalshi on Politics by a wide margin, holding 92.6% of combined cross-platform political notional volume. Both platforms saw politics volume soften week-over-week with Kalshi down 9.9% and Polymarket Politics + Trump down 8.1%, but the absolute levels remain vastly different. Polymarket’s slate was anchored by the US-Iran peace deal, both 2028 presidential nomination markets, and the 2028 presidential election.
Kalshi’s politics activity has a more domestic makeup, driven last week by LA Mayor, California Governor, and House control in 2026 midterms, with no individual market approaching Polymarket’s top politics volumes. Interesting to note that Kalshi’s 2028 Democratic Nominee market carries substantial open interest on comparatively light weekly flow, pointing to long-duration positioning rather than active trading.
What we’re watching
The post-Masters dip we flagged for the week of April 13 looked like a potential inflection point, but Kalshi bounced to a new record while Polymarket has continued lower. Going into May, the question is how the NBA Finals and the 2026 FIFA World Cup, which kicks off in June, shift the balance. World Cup markets are already showing $327.2 million in 30-day trading volume, with 99.3% coming from Polymarket according to our tracker.
Kalshi’s game and series markets, combined with parlay depth, positions it well to sustain current levels through the NBA Finals and Stanley Cup Finals. How each platform captures World Cup volume will be a defining test in the sports category this summer. Meanwhile, the PGA championship is this week, and the French Open kicks off next week, two major volume drivers especially for Kalshi.
