Kalshi posted a new volume record for the week of March 9-15, surging to $2.9B on the back of NCAAB conference tournaments. Meanwhile, Polymarket dipped 6% ahead of the March fed meeting.
The weekly total dipped slightly, but the more telling story is Kalshi and Polymarket moved in opposite directions this week, driven by unrelated forces. Kalshi posted $2.93B in notional volume, its highest single-week total in the DeFi Rate tracking period, while Polymarket pulled back to $2.34B. Together they totaled $5.28B for the week of March 9–15, down modestly from $5.35B the prior week, as total industry volume across all tracked platforms hit $5.76B.
- Kalshi: $2.93B weekly volume (+2.7% WoW)
- Polymarket: $2.34B weekly volume (-6.1% WoW)
Across all tracked platforms, 44.4 million transactions were recorded for the week. The DeFi Rate prediction markets tracker has the full breakdown, including open interest by platform and category. Kalshi’s gains came almost entirely from conference championship basketball — four college games cracked its weekly top 10 ahead of Selection Sunday — while Polymarket’s most active market was a Federal Reserve rate decision that drew $141.9M over the previous seven days.
Some key takeaways from last week:
- NCAA basketball games appeared in Kalshi’s top 10 for the first time, with Wisconsin-Michigan leading at $9.2M as March Madness trading gets ready to ramp up.
- Three 2028 presidential markets on Polymarket combined for $121.5M, a meaningful volume driver with the election over two years out.
- The Oscars helped drive WoW surges in Entertainment trading volume on both Kalshi (326%) and Polymarket (96%), though the category remains small compared to Sports and Crypto category volumes on both platforms.
Kalshi vs. Polymarket trend
Kalshi extended its run of majority market share relative to Polymarket, adding $76.6M WoW (+2.7%) while Polymarket dropped $152.1M (-6.1%). The divergence traces cleanly to the sports calendar. Conference championship week with the Big Ten, SEC, Mountain West, and other major tournaments running simultaneously delivered a wave of short-duration, high-liquidity basketball markets that play directly to Kalshi’s strength in domestic sports outcomes.
On transactions, Polymarket still leads: 24.7 million trades versus Kalshi’s 19.7 million. Both platforms shed transactions WoW (Kalshi -1.5%, Polymarket -6.1%) meaning this week’s volume moves came from larger individual positions, not more activity. That reads clearly in the average bet sizes: Kalshi traders averaged $148.61 per trade (+4.2% WoW) while Polymarket came in at $95.01, essentially flat. The 1.6:1 ratio in average bet size has been a consistent feature across recent weeks, reflecting meaningfully different participant behavior. Polymarket is attracting higher-frequency, smaller-bet traders while Kalshi skews toward larger individual positions on a per-trade basis.
55.6%
Kalshi share (vs. Poly)
| Week of | Kalshi vol. | Poly vol. | Kalshi WoW | Poly WoW |
|---|---|---|---|---|
| Feb 2 | $2.80B | $1.92B | — | — |
| Feb 9 | $2.43B | $1.88B | -13.2% | -1.9% |
| Feb 16 | $2.59B | $1.82B | +6.8% | -3.2% |
| Feb 23 | $2.73B | $2.40B | +5.3% | +31.9% |
| Mar 2 | $2.86B | $2.50B | +4.7% | +4.0% |
| Mar 9 | $2.93B | $2.34B | +2.7% | -6.1% |
Market share settled at 55.6% Kalshi, 44.4% Polymarket on a head-to-head basis, continuing a trend that carried from NFL into a dense NBA and NCAA basketball schedule. The structural question heading into Q2 is whether Kalshi can hold majority share once the college basketball season ends and the NBA heads into playoffs mode in April.
Kalshi vs. Polymarket metrics: Week of March 9-15
| Metric | Kalshi | WoW Δ | Polymarket | WoW Δ |
|---|---|---|---|---|
| Volume | $2.93B | +2.7% | $2.34B | -6.1% |
| Transactions | 19,747,251 | -1.5% | 24,671,808 | -6.1% |
| Avg. bet size | ~$148.61 | +4.2% | ~$95.01 | ~flat |
| Market share | 55.6% | — | 44.4% | — |
Source: DeFi Rate. Week ending March 15
Polymarket US highlights
Polymarket US remains sports-only and currently basketball-focused. All 10 highest-volume markets last week were NBA or college basketball game outcomes. The top market — Sacramento Kings vs. Los Angeles Clippers — drew $590.2K; the bottom of the top 10 came in at $341.1K (Golden State Warriors vs. Utah Jazz).
The volume scale gap between Polymarket US and either Kalshi or global Polymarket remains wide: the top US market this week represents roughly 1/23rd the volume of the comparable Kalshi NBA game.
Polymarket US weekly snapshot
| Metric | Mar 9–15 | Mar 2–8 | WoW Δ |
|---|---|---|---|
| Volume | $5.9M | $5.9M | ~flat |
| Active markets | 488 | 354 | +37.9% |
| Open interest | $1.1M | $884.4K | +24.4% |
| Top market | Sacramento vs. LA Clippers | OKC vs. NY Knicks | — |
| Top market volume | $590.2K | $532.9K | +10.7% |
Source: DeFi Rate prediction markets tracker. Week ending March 15
While overall volume was flat, active markets up 37.9% to 488 and open interest up 24.4% to $1.1M both suggest the platform is expanding its market coverage even as raw volume holds steady.
Polymarket US top 5 markets by volume, last 7 days
| # | Market | Leading | Volume (7d) |
|---|
All markets are NBA or college basketball game outcomes. All closed.
Category breakdown: Kalshi vs. Polymarket
The Oscars aired on March 15, the final day of the reporting window, and drove a late-week volume spike on both platforms that inflated what would otherwise have been modest numbers in those categories. Kalshi’s Entertainment category surged 326% to $62.3M and Polymarket’s Culture category nearly doubled to $59.1M (+95.8%), primarily due to trading on Oscars markets. Expect the category to normalize this week.
Strip out the Oscars effect and the Kalshi picture is defined by two diverging forces. Sports grew 5.0% to $2.09B, continuing its steady climb through conference tournament week, while Exotics cratered 33.0% to $256.4M after the prior week’s parlay-driven surge. Those two moves largely offset each other within Kalshi’s overall category mix. Politics and Elections categories combined fell 69.6% to $24.0M, reflecting the absence of a single high-profile event market like the prior week’s Khamenei contracts. Crypto dipped modestly, down 9.7% to $233.6M.
On Polymarket global, Politics climbed 17.6% to $598.0M as the 2028 presidential markets deepened and the Fed decision contract dominated the top of the board. But that growth masked a 52.5% collapse in the Trump-specific category ($157.0M → $74.5M). Combined, politics-adjacent volume was essentially flat week over week ($665.7M → $672.5M), but shifted away from Trump-specific markets. Sports fell 9.1% to $925.4M, giving back some of last week’s gains, while Crypto declined 13.5% to $625.7M alongside a softer week for Bitcoin price action.
The structural cross-platform picture holds. Kalshi runs 71% sports (actually more with exotics included); Polymarket runs 61% non-sports. Kalshi’s non-sports total was $841.3M this week; Polymarket’s was $1.4B. The two platforms are drawing on different audiences for different purposes, and this week’s data continued that trend.
Kalshi vs. Polymarket category volume: This week vs. last week
Top markets: Kalshi & Polymarket
Kalshi’s top 10 is entirely basketball, with six NBA games and four NCAAB conference tournament matchups. The NBA side of the list is led by marquee matchups — NY Knicks at Clippers at $13.7M, Nuggets at Thunder at $12.9M, Timberwolves at Lakers at $10.8M — but the college entries are the more notable development. Wisconsin-Michigan ($9.2M), New Mexico–San Diego State ($9.0M), and Oklahoma–Arkansas ($8.9M) each traded at volume levels comparable to the largest NBA games on the list. Vanderbilt’s upset win over Florida at $7.9M was also among Kalshi’s top markets.
Polymarket’s top 10 shares almost nothing with Kalshi’s. The Fed’s March rate decision topped the list at $141.9M, a single market larger than Kalshi’s entire top 10 combined ($97.4M), with $50.8M in open interest still live ahead of the March 17 close. Three 2028 presidential markets followed at $50.6M, $42.0M and $28.9M. Only a pair of sports futures markets snuck into Polymarket global’s top 10 this week: the FIFA World Cup winner ($29.1M) and Champions League winner ($18.6M), both active through mid-year.
Kalshi top 10 markets by volume, last 7 days
| # | Market | Volume (7d) |
|---|---|---|
| 1 | New York at Los Angeles Clippers | $13.7M |
| 2 | Denver at Oklahoma City | $12.9M |
| 3 | Minnesota at Los Angeles Lakers | $10.8M |
| 4 | Golden State at Utah | $9.4M |
| 5 | Wisconsin at Michigan | $9.2M |
| 6 | New Mexico at San Diego State | $9.0M |
| 7 | Oklahoma at Arkansas | $8.9M |
| 8 | New York at Utah | $7.9M |
| 9 | Vanderbilt at Florida | $7.9M |
| 10 | Boston at San Antonio | $7.8M |
Source: DeFi Rate
Polymarket top 10 markets by volume, last 7 days
| # | Market | Volume (7d) | Open int. |
|---|---|---|---|
| 1 | Fed decision in March? | $141.9M | $50.8M |
| 2 | Republican Presidential Nominee 2028 | $50.6M | $11.1M |
| 3 | Democratic Presidential Nominee 2028 | $42.0M | $8.5M |
| 4 | 2026 FIFA World Cup Winner | $29.1M | $2.0M |
| 5 | Presidential Election Winner 2028 | $28.9M | $3.9M |
| 6 | UEFA Champions League Winner | $18.6M | $3.3M |
| 7 | Will Crude Oil hit $__ by end of March? | $17.7M | $8.3M |
| 8 | What price will Bitcoin hit in March? | $17.6M | $9.4M |
| 9 | 2026 NBA Champion | $17.5M | $729.3K |
| 10 | Netanyahu out by…? | $17.3M | $9.3M |
Source: DeFi Rate
Full platform volume comparison
Overall prediction market industry volume based on Dune Analytics tracked platforms reached $5.76B for the week of March 9–15, down $133.9M (-2.3%) from the prior week’s $5.89B. The decline was concentrated in Opinion Markets, which fell 50.0% WoW to $77.9M — its fifth consecutive weekly drop and a 94%+ retreat from its $1.81B peak in late December.
Excluding Opinion, remaining tracked platforms were up slightly on aggregate. Crypto.com (+27.3% to $156.1M) and predict.fun (+18.1% to $91.2M) were the week’s strongest performers by WoW growth rate among named platforms.
March Madness expected to lift the tides
Selection Sunday took place on March 15, setting the 64-team bracket for the 2026 NCAA Tournament. First- and second-round games run March 19–22, after First Four play-in games March 17-18. March Madness markets historically generate some of the most concentrated sports volume of the calendar year with short windows, high stakes, and upset-friendly formats that produce significant two-sided action on the majority of games.
Kalshi’s conference tournament performance this week suggests the demand is already priced in. Four tournament-week games cracked the weekly top 10 before the bracket was finalized, trading at volume levels comparable to the platform’s most active NBA games. March Madness could push Kalshi above $3.5B in a single week, a threshold it has not yet reached. We will also be watching for whether Polymarket can close the gap with its own NCAAB surge, and how much growth its US platform can achieve across the action-packed March Madness schedule.
Valerie Cross
Valerie Cross is a reporter, editor, and prediction markets analyst with more than a decade of experience covering legal gaming and emerging financial markets. She joined DeFi Rate in 2026 after reporting on the rise of mainstream prediction markets and previously held senior editorial roles at Prediction News and Catena Media. Valerie holds a BA from Furman University and MA and PhD degrees from Indiana University.
