Kalshi has already posted $12.35 billion in notional volume in March 2026, surpassing its previous all-time high of $10.44 billion set during Super Bowl month in February. It’s an 18.3% month-over-month jump with two days of volume still to collect for March. Meanwhile, Polymarket’s global platform has exceeded $10 billion in monthly volume for the first time, outpacing its previous all-time high of $7.94 billion, also set in February.

The result makes March the single largest month for both Kalshi and Polymarket, with Kalshi’s new record also representing the biggest month ever recorded by a U.S.-regulated prediction market exchange.

The NCAA Tournament was the main driver for Kalshi. All ten of Kalshi’s top markets by volume in March were college basketball games, with Duke matchups alone accounting for four of them. The Elite Eight game between UConn and Duke on March 29 led the platform with $24.5 million in combined contract volume. Notably, a First Round matchup, Siena at Duke, generated $18.1 million, more than most Sweet 16 games, reflecting the enormous speculative interest in a potential 15-seed upset of the tournament’s biggest draw.

On a weekly basis, the March 16 week, encompassing Selection Sunday through the first two rounds, is still the single largest week in the dataset at $3.40 billion, edging out even the bracket’s later rounds.

Note: Kalshi and Polymarket US and global volume data and top markets pulled from our internal prediction markets tracking data. Other platform data and category totals are from Dune.

Kalshi continues to track above Polymarket in terms of total notional volume, driven in large part by the sports calendar. Still, Polymarket’s $10.15 billion in global notional volume through the first 29 days of March surpasses its prior monthly record of $7.94 billion set in February for a 27.8% increase and the largest month-over-month dollar gain of any platform this month. Polymarket’s unique user count hit 768,476 month to date, up 14.4% already from February’s 671,441.

Both platforms posted their best months ever in March, but by different routes. Kalshi’s $12.35 billion edged Polymarket’s $10.15 billion globally, a $2.2 billion difference, though Polymarket’s 27.8% MoM volume growth outpaced Kalshi’s 18.3%, driven by a surge in geopolitical trading activity. Polymarket’s transaction growth was even more pronounced, up 36.3% versus Kalshi’s 17.4%, suggesting a higher volume of smaller trades on the crypto-native platform compared to Kalshi’s larger average contract sizes.

Week over week, both platforms tracked closely through March, peaking in the March 16 week before pulling back in the final full week of the month.

The week of March 16 is still Kalshi’s best week ever, thanks to a whopping 52 games packed into the first six days of the men’s NCAA basketball tournament. That included the first four play-in games plus 32 Round 1 games and 16 Round 2 games. Last week’s Sweet 16 (eight games) and Elite 8 (four games) still drove significant volume last week, but not near the cumulative volume as Week 1 of March Madness.

Polymarket’s peak was less pronounced, reflecting its heavier reliance on geopolitical rather than sports-driven volume. The March 23 pullback on both platforms is to be expected with 12 total men’s March Madness games vs. the previous week’s 52.

Where Kalshi’s volume was driven by sports, Polymarket’s top markets were dominated by Middle East geopolitics. The top three markets by volume were all Iran-related: Khamenei out as Supreme Leader by February 28 ($125M), US strikes Iran by February 28 ($84M), and Netanyahu out by March 31 ($81M). The contrast illustrates the fundamentally different audiences the two platforms serve with American sports bettors on one side, and crypto-native international traders on the other.

That divergence shows up clearly in the category-level data. Sports continues to dominate on Kalshi’s end, accounting for 87% of volume over the last four weeks (March 2-29), $9.90 billion of $11.38 billion. That includes the newly separated out “Exotics” category, comprising primarily of sports parlay or “combo” volume.

Polymarket’s volume was more evenly distributed, with Politics (including Trump markets) at $2.97 billion and Crypto at $2.72 billion together making up 57% of its total. In the one category where both platforms compete directly, Sports, Kalshi’s $9.90 billion was 2.5x Polymarket’s $4.03 billion.

Total prediction market volume with two days to go reached $24.47 billion in March across all tracked platforms, up from $23.25 billion in February. Four platforms set simultaneous all-time highs: Kalshi, Polymarket, Crypto.com ($598M, up 50.5% from its prior ATH of $452M in January), and Limitless ($456M). The multi-platform record performance suggests broad market expansion rather than simple rotation between platforms.

Total industry transactions for March already exceeded February’s full-month count of 155.7 million, with 188.1 million recorded across just the first four weeks.

The one significant drag on headline totals was Opinion, which fell from $3.11 billion in February to $475 million in March for an 84.7% drop. Opinion Labs’ volume figures, which we flagged as likely highly inflated, are thus skewing the month-over-month industry totals on Dune. Without that decline, total market growth would have been substantially larger.

For context on the U.S. regulatory landscape, Polymarket’s domestic product recorded $232 million in March volume across 4,597 markets, according to our tracking. Polymarket US remains in early buildout, still with sports markets only, while its top domestic competitor Kalshi continues to operate at scale. The Kalshi domination of US prediction market trading volume is unlikely to change any time soon, though challengers are lining up to give it a shot.

The post Kalshi Hits $12B, Polymarket $10B All-Time Highs on March NCAA Tournament Surge appeared first on DeFi Rate.

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