Kalshi widened its lead over Polymarket in weekly prediction market trading volume, accounting for 70.8 per cent of total activity during the week of May 18. The CFTC-regulated exchange processed nearly $4 billion in notional volume as Polymarket recorded a sharp weekly decline.
Prediction markets allow users to trade contracts tied to the outcome of future events, including elections, sports, and crypto prices. Kalshi posted $3.99 billion in notional volume during the week of 18 May, up 3 per cent from the previous week, according to DeFi Rate’s volume tracker. Polymarket fell 15 per cent to $1.65 billion, down from $1.94 billion during the week of 11 May. Combined weekly notional volume across Kalshi and Polymarket reached $5.64 billion for the week of 18 May, down around 3.1 per cent from the previous week.
Kalshi nears another monthly volume record
With one week remaining in May, Kalshi has generated around $12 billion across the first three reported weeks of the month, putting the exchange within reach of the $14.81 billion monthly volume record it set in April. Polymarket has generated around $5.19 billion over the same period, leaving it well short of the pace needed to challenge its March record of $10.57 billion.
Kalshi’s latest weekly performance kept the exchange near the $4 billion level for a third consecutive week in May. The platform reached $4.13 billion during the week of 4 May, dipped to $3.88 billion during the week of 11 May, and climbed back to $3.99 billion during the week of 18 May. By contrast, Polymarket moved in the opposite direction after a stronger week earlier in May. Its 15 per cent weekly decline widened Kalshi’s lead in the ongoing Kalshi vs Polymarket battle. Polymarket has not topped $2 billion in weekly notional trading volume since the week of 13 April.
While global Polymarket volume declined, Polymarket US posted a different trend. The US-facing platform recorded a 7.5 per cent increase to $447.7 million. Transaction activity rose on both prediction market platforms. Kalshi processed 25.8 million transactions, up 7.3 per cent week on week, while Polymarket processed 17.4 million transactions, up 0.9 per cent.
Sports continue to dominate prediction markets
Sports remained the largest category across both platforms, though Kalshi and Polymarket continued to show sharply different trading mixes. Kalshi’s volume was more concentrated in sports and exotics, a category widely understood to capture parlay-style sports markets known as combos. Polymarket showed a more balanced split across sports, crypto, and politics. Kalshi generated around $1.59 billion in sports-related volume, compared with $675.5 million for Polymarket in the same category.
In crypto markets, the two prediction market platforms were more closely matched, with Polymarket slightly ahead. Politics remained a much larger driver for Polymarket, where political contracts significantly outpaced Kalshi’s political market activity.
India and Indonesia tighten prediction market scrutiny
India is expected to formally block prediction market platforms Kalshi and Polymarket in a fresh crackdown on offshore operators that remain accessible despite India’s online gaming ban. Indian regulators have increasingly viewed event-based contracts as prohibited online money gaming activities. The latest warning comes as Kalshi and Polymarket continue accepting Indian users despite earlier regulatory concerns.
Indonesia recently blocked Polymarket, describing the service as a form of online gambling. Indonesia’s Ministry of Communication and Digital Affairs (Komdigi) said authorities blocked the platform over concerns it facilitated money-based betting on uncertain outcomes. Meanwhile, South Korea is actively reviewing whether Polymarket hosts illegal gambling content.
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